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darmstadtium

The Quark Matter 2014 conference is the twenty-fourth edition of the most prestigious series of international meetings in the field of ultrarelativistic heavy-ion collisions. The meetings bring together theorists and experimentalists committed to understanding the fundamental properties of strongly interacting matter at extreme energy densities. The conditions reached in head-on nuclear collisions at the highest currently available energies correspond to those in primordial matter a few tens of microseconds after the Big Bang. Thus, this type of laboratory research improves our understanding of the early phase of the Universe.

The first Quark Matter conference took place in 1980 in Darmstadt. Since then, the meetings of this series have been organized approximately every 1.5 years. The recent instances were in Jaipur, India (2008), Knoxville, USA (2009), Annecy, France (2011), and Washington DC, USA (2012). The current meeting brings the conference to Darmstadt again, a place with a long-standing tradition of heavy-ion research and is jointly organized by GSI Helmholtzzentrum für Schwerionenforschung GmbH, Technische Universität Darmstadt, and Universität Heidelberg.

europium

darmstadtium

Measurement of the centrality dependence of the charged particle pseudorapidity distribution in proton-lead collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with the ATLAS detector20m

Proton-lead collisions at the LHC provide an opportunity to probe the
physics of the initial state of ultra-relativistic heavy ion
collisions. In particular, they can provide insight on the effect
of an extended nuclear target on the dynamics of soft and hard
scattering processes and subsequent particle production. Charged
particle multiplicity and pseudorapidity distributions are among
the most basic experimental probes of particle production.
The centrality dependence of the charged particle pseudorapidity
distributions, dNch/deta , was measured in p+Pb collisions at a
nucleon-nucleon centre-of-mass energy of sqrt(s_NN) = 5.02 TeV using
the ATLAS detector. Charged particles were reconstructed over |eta| <
2.7 using the ATLAS pixel detector. The proton-lead collision
centrality was characterized by the total transverse energy measured
over the pseudorapidity interval 3.2 < eta < 4.9 in the direction of
the lead beam. The dNch/deta distributions are found to vary strongly
with centrality, with an increasing asymmetry between the proton-going
and Pb-going directions as the collisions become more central. Three
different calculations of the number of participants, Npart, have been
carried out using a standard Glauber model as well as two
Glauber-Gribov extensions. Charged particle multiplicities per
participant pair are found to vary differently with Npart for these
three models, highlighting the importance of the fluctuating nature of
nucleon-nucleon collisions in the modeling of the initial state of
p+Pb collisions.

Transverse energy distributions at mid-rapidity in $p$$+$$p$, $d$$+$Au, and Au$+$Au collisions at $\sqrt{s_{NN}} = $62.4--200 GeV and implications for particle production models20m

Measurements of the midrapidity transverse energy distribution
$dE_T/d\eta$, are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au
collisions at 62.4--200 GeV. The $E_T$ distributions are compared with
the number of participants, $N_{\mathrm{part}}$, the number of binary
collisions, $N_{\mathrm{coll}}$, and the number of constituent-quark
participants, $N_{qp}$, calculated from a Glauber model. For Au$+$Au,
$(dE_T/d\eta)/N_{\mathrm{part}}$ indicates that the two component
ansatz $dE_T/d\eta ~ (1-x)N_{\mathrm{part}}/2+xN_{\mathrm{coll}}$, which
has been used to explain $E_T$ distributions is simply a proxy for
$N_{qp}$, and that the $N_{\mathrm{coll}}$ term does not represent a
hard-scattering component in $E_T$ distributions. The $dE_T/d\eta$
distributions of Au$+$Au and $d$$+$Au are then calculated from the
measured $p$$+$$p$ $E_T$ distributions using two models (additive
quark model and the number-of-constituent quarks model) that both
reproduce the Au$+$Au data. However, the
number-of-constituent-quark-participant model agrees well with the
$d$$+$Au data, while the additive quark model does not. A description
of the various models and their implications will be discussed.

Speaker:
Michael Tannenbaum
(Brookhaven National Laboratory (US))

Slides

11:40

Collective flow in small systems20m

The collective expansion of the fireball formed in ultrarelativistic p-A and d-A collisions are discussed. Estimates based on the extrapolation of the hydrodynamic model from A-A collisions to small systems indicate possible formation of a dense droplet of matter. Fluctuation in the initial state lead to finite eccentricity and triangularity, which give measurable elliptic and triangular flow of the emitted particles. Further predictions consistent with experimental observations are the mass ordering of the average transverse momentum and of the elliptic flow for identified particles. We discuss the prediction of the model for collisions of a deformed projectile as in d-A collisions. This deformation leads to a large elliptic flow.

Speaker:
Piotr Bozek

Slides

12:00

Light flavor hadron spectra at low-$p_{\rm T}$ and search for collective phenomena in high multiplicity pp, p-Pb and Pb-Pb collisions measured with the ALICE experiment20m

Comprehensive results on transverse momentum distributions, their ratios, d$N$/d$y$ and <$p_{\mathrm{T}}$> values for identified light flavor hadrons ($\pi$, K, p, $\Lambda$, $\Xi$, $\Omega$) at low $p_{\mathrm{T}}$ and mid rapidity are reported for all collision systems at LHC energies: pp, p-Pb, Pb-Pb. It is well known that strong collective effects are observed in central Pb-Pb collisions as a particle mass dependent hardening of the spectral shapes attributed to hydrodynamical flow and may be quantitatively parametrized with Boltzmann-Gibbs Blast Wave fits. In this talk, we investigate the existence of collective phenomena in small systems: pp, p-Pb and peripheral Pb-Pb where similar patterns are observed in multiplicity dependent studies. For pp collisions, measurements at three center-of-mass energies ($\sqrt{s} = $ 0.9, 2.76, 7 TeV) are presented and the evolution of the spectral shape with $\sqrt{s}$ is discussed.

In this talk the transverse momentum spectra of identified particles, geometry categorization and bias, and global observables in d+Au collisions at 200 GeV are reported. In d+Au collisions, the intermediate $p_T$ region between 2 and 5 GeV, there is a significant enhancement of the baryon to meson ratios relative to those measured in p+p collisions. The enhancement is present in d+Au collisions as well as Au+Au collisions and increases with centrality. We compare a class of peripheral Au+Au collisions with a class of central d+Au collisions which have a comparable number of participants and binary collisions. The $p_T$ dependent ratios for these classes display a remarkable similarity. The nuclear modification of hadrons at higher transverse momentum also reveal interesting effects. Geometry selection in d+Au/p+Pb collisions is crucial for understanding the physics underlying modified nuclear parton distribution functions, gluon saturation and glasma diagrams, initial state energy loss, and possible hydrodynamic flow in these small systems. Data from the p+Pb LHC results indicate potentially large biases in the geometry determination in these small systems. The PHENIX collaboration presents tests of auto-correlation biases. Our findings indicate that these biases are an order of magnitude smaller at RHIC as compared to the LHC, and are thus well quantified. Geometry tests with neutron-tagged events and the centrality scaling of d$N_{ch}/d\eta$ and d$E_T/d\eta$ are presented.

Speaker:
Sarah Campbell
(Iowa State University)

Slides

12:40

Why is the radial flow in high multiplicity pp/pA stronger than in AA?20m

With growing multiplicity, the pp and pA collisions enter the domain where the macroscopic description (thermodynamics and hydrodynamics) becomes applicable. We discuss this situation, first with simplified thought experiments, then
with some idealized representative cases, and finally address the real data.
For clarity, we don't do it numerically but analytically, using the Gubser solution.
We found that the radial flow is expected to increase from central AA to central pA.
Recent CMS and ALICE data confirm that it is the case. We discuss the
consequences of these finding.

Speaker:
Edward Shuryak
(stony brook university)

Slides

11:00
→
13:00

Electromagnetic probes: 1helium

helium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Charles Gale
(McGill University)

slides

11:00

Beam energy dependence of dielectron production in Au+Au collisions from STAR at RHIC20m

Bulk-penetrating dielectrons allow for the extraction of direct information
from all stages of a heavy ion collision as they serve as electromagnetic
probes with negligible final-state interactions. The completion of the Barrel
Time-of-Flight detector (TOF) in 2010 has allowed the Solenoid Tracker At
RHIC (STAR) to play a unique role in the study of dielectron production with
excellent particle identification, low material budget, full azimuthal
acceptance at mid-rapidity, and a wide momentum coverage. In combination with
the Beam Energy Scan (BES) conducted at RHIC, in particular, STAR presents the
unprecedented opportunity to map out a significant portion of the QCD phase
diagram within a homogeneous experimental environment. In the quest for a
better understanding of strongly interacting nuclear matter the Low-Mass Region
(LMR, $M_{ee}$ < 1.1 GeV/$c^2$) of dielectron spectra, on the one hand, provides information about in-medium modifications of the $\rho$-meson's
properties. The Intermediate-Mass Region (IMR, 1.1 < $M_{ee}$ < 3
GeV/$c^2$), on the other hand, can provide access to the initial
Quark-Gluon Plasma (QGP) temperature as well as a possibly medium-modified
correlated charm continuum.
In this talk, we will present the energy-dependent study of dielectron
production at $\sqrt{s_{NN}}$ of 19.6, 27, 39, and 62.4 GeV. $M_{ee}$ and $p_{\text{T}}$ differential measurements of LMR mass distributions are compared to cocktail simulations of known hadronic sources. The excess yield is further
compared to calculations of $\rho$ in-medium modifications.
Properties of IMR spectral data will be compared to simulations of
semi-leptonic charmed decays.

Speaker:
MrPatrick Huck
(LBNL/CCNU)

Slides

11:20

Dielectron measurements in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC20m

Electromagnetic probes are excellent messengers from the hot and dense medium
created in ultra-relativistic heavy-ion collisions. Since leptons do not interact
strongly, their spectra reflect the entire space-time evolution of a
collision. The surrounding medium can lead to modifications of the dielectron
production rate. To quantify modifications in heavy-ion collisions, measurements
in pp collisions serve as a reference, while the analysis of p-A collisions
allows to disentangle cold from hot nuclear matter effects.
We present dielectron measurements with the ALICE central barrel detectors. The
invariant mass distributions in the range $ 0 < m_{ee} < 3 $ GeV/$ c^{2} $ are
compared to the expected hadronic sources for pp collisions at $ \sqrt{s}=7 $
TeV, and for p-Pb collisions at $ \sqrt{s_{\rm NN}} = 5.02$ TeV. The cross
section of virtual direct photons measured in pp collisions is compared to
predictions from NLO calculations as a function of the transverse momentum.
Latest results of the analysis of Pb-Pb collisions at $ \sqrt{s_{\rm NN}}=2.76 $
TeV are presented.

I will discuss the general features of the electromagnetic radiation from QCD matter using spectral functions in the hadronic phase and
the OPE expansion in the partonic phase, and use them to analyze
current di-lepton and photon emissions at collider energies both at RHIC and LHC. The large low mass di-lepton enhancement and photon
v2 will be addressed.

Speaker:
MrIsmail Zahed
(Stony Brook University)

Slides

12:00

Thermal photon $v_3$ at LHC from event-by-event hydrodynamics20m

Thermal photon $v_3$ is calculated for 0--40% central collisions of Pb nuclei at LHC from event-by-event ideal hydrodynamic model [1]. The differential triangular flow parameter $v_3(p_T)$ calculated with respect to the participant plane (PP) is found to be non-zero, positive, and shows similar qualitative nature to the elliptic flow parameter $v_2(p_T)$ [2]. At $p_T=$ 1 GeV $v_3$(PP) is found to be about half of $v_2$(PP) however, for larger values of $p_T$ these two anisotropy parameters become comparable. The global geometry of the produced matter as well as the local fluctuations in the initial density distribution are responsible for this substantial value of the triangular flow parameter for thermal photons where $v_3$(PP) probes the initial state geometry in an indirect way via the generation of additional transverse flow. $v_3$ calculated with respect to the reaction plane as expected is close to zero. $v_3$(PP) strongly depends on the value of the fluctuation size parameter $\sigma$ especially in the higher $p_T$ region where, a larger $\sigma$ results in a smaller $v_3$(PP). In addition, the $v_3$(PP) is found to increase with the initial formation time of the system.
[1] R. Chatterjee, D. K. Srivastava, and T. Renk, arXiv:1401.7464.
[2] R. Chatterjee, H. Holopainen, I. Helenius, T. Renk, and K. J. Eskola, PRC88, 034901 (2013).

Speaker:
Rupa Chatterjee

Slides

12:20

Viscous corrections to photon emission in heavy-ion collisions20m

Photons are believed to be clean and penetrating probes of the medium created in ultra-relativistic heavy-ion collisions. The thermal photon spectrum and its anisotropy coefficients, $v_n$, are known to be very sensitive to the thermalization time, the specific shear viscosity, the equation of state of produced matter, and the initial state fluctuations [1,2]. In this talk, we will present state-of-the-art calculations of event-by-event photon emission from nuclear collisions at RHIC and LHC energies including both shear and bulk viscous corrections. Momentum spectra of thermal photons and their $p_T$-differential anisotropic flow coefficients $v_n(p_T)$ ($n$ up to 5) are computed, both with and without accounting for viscous corrections to the standard thermal emission rates. Viscous corrections to the rates are found to have a larger effect on the $v_n$ coefficients than the viscous suppression of hydrodynamic flow anisotropies. Effects from non-zero initial flow and viscous pressure tensor to photon spectra and their anisotropies are also investigated by evolving fluctuating initial density profiles with free-streaming on the event-by-event basis before matching to hydrodynamics. Complementary to the majority of hadronic observables, thermal photons provide us with additional constraints on the evolution of the viscous pressure tensor as well as the early dynamics of heavy-ion collisions. Their anisotropic flows, especially higher order $v_n$, can be used as a sensitive viscometer for the quark-gluon plasma.
[1] C. Shen, U. Heinz, J.-F. Paquet and C. Gale, "Thermal photons as a quark-gluon plasma thermometer revisited", arXiv:1308.2440 [nucl-th].
[2] C. Shen, U. Heinz, J.-F. Paquet, I. Kozlov and C. Gale, "Anisotropic flow of thermal photons as a quark-gluon plasma viscometer", arXiv:1308.2111 [nucl-th].

Experimental measurements of photon collective flow have obtained v2 comparable to those of hadrons. This favors a scenario of hadron dominated medium in photon production. A realistic calculation of photon rate in QGP phase is important to scrutinize this scenario. Fire ball produced in RHIC and LHC is close to semi-QGP which has a non-trivial value of Polyakov loop. We calculated the photon rate in the semi-QGP and found indeed a suppression of the photon rate due to non-trivial Polyakov loop, as compared to standard thermal perturbative results. We also calculated dilepton rate in the same semi-QGP. On the contrary, we found non-trivial Polyakov loop enhances the dilepton rate. This implies the v2 of dilepton distinguishes from that of photon.

Speaker:
Shu Lin
(RIKEN BNL)

Slides

11:00
→
13:00

Heavy flavor: 1platinum

platinum

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Joerg Aichelin
(University of Nantes)

announcement

11:00

Theoretical predictions of jet suppression: a systematic comparison with RHIC and LHC data20m

Accurate theoretical predictions of jet suppression are necessary for studying the properties of QCD matter created in ultra-relativistic heavy ion collisions. However, testing the prediction accuracy - and extracting useful qualitative knowledge - is often limited by constraining the predictions to only few experimental probes at a time, and by using free parameters. To address this issue, we will present comprehensive suppression predictions, which run across all available probes and different centrality regions at RHIC and LHC. To generate these predictions, we use the finite size dynamical QCD formalism that we previously developed, together with its recent extensions to finite magnetic mass [1] and running coupling [2]; this formalism is integrated into a numerical procedure that uses no free parameters in model testing. We obtain a very good agreement with the experimental results across all particle species [2,3], for different centrality regions [4], and for both RHIC and LHC. We will also discuss improved qualitative understanding of the relevant experimental data, which follows from such comprehensive comparison.
1. M. Djordjevic and M. Djordjevic, Physics Letters B 709, 229 (2012).
2. M. Djordjevic and M. Djordjevic, arXiv:1307.4098
3. M. Djordjevic, Phys.Rev.Lett. 112, 042302 (2014).
4. M. Djordjevic, M. Djordjevic and B. Blagojevic, to be submitted.

Speaker:
DrMagdalena Djordjevic
(Institute of Physics Belgrade, University of Belgrade)

Slides

11:20

Heavy quark physics measurements with the PHENIX Detector20m

In heavy ion collisions at RHIC, heavy quarks are produced predominantly in the initial hard scatterings and thus probe the entire lifetime of the hot and dense medium. Additionally, measuring charm and beauty quarks allows us to study the mass dependence of energy loss, constraining the transport properties of the Quark-Gluon Plasma. Previous measurements at RHIC have shown large suppression and azimuthal anisotopy of open heavy flavor hadrons. In order to further constrain medium properties using heavy flavor probes, the interaction of charm and beauty quarks must be measured separately. PHENIX presents new results on heavy quark physics via single leptons, dilelectron correlations, electron-muon correlations, and tagging with displaced vertices.

Speaker:
Alan Dion
(Stony Brook University)

Slides

11:40

Heavy-flavour production and nuclear modification factor in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ =2.76 TeV with ALICE20m

Heavy quarks (charm and beauty) are considered effective probes to investigate the properties of the strongly-interacting medium formed in high energy nuclear collisions. Heavy quarks lose energy interacting with the medium via inelastic processes (medium-induced gluon radiation) and elastic collisions. The nuclear modification factor, $R_{\rm AA}$, defined as the ratio of the heavy-flavour production yield in nucleus-nucleus collisions to the binary scaled pp one, is an observable sensitive to in-medium energy loss. In particular, the comparison of the $R_{\rm AA}$ of charm, beauty and light-flavour hadrons provides information about the colour charge and parton mass dependence of the energy loss.
Open heavy-flavour production was measured with ALICE in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76~\mathrm{TeV}$ using D mesons ($ {\rm D^0} $, ${\rm D^{*+}}$, $ {\rm D^{+}} $ and ${\rm D_s^+}$ ) reconstructed from their hadronic decays and electrons from heavy-flavour decays at central rapidity, and muons from heavy-flavour decays at forward rapidity. The D meson and heavy-flavour decay leptons differential $ R_{ \rm AA } $ measurements, namely the transverse momentum, rapidity and centrality dependence, will be shown. The comparison of the nuclear modification factors of strange and non-strange D mesons will be presented, as well as the ${\rm D^0}$ $R_{\rm AA}$ measured in different azimuthal regions with respect to the reaction plane of the collision. The D meson $R_{\rm AA}$ will be compared with light-flavour and non-prompt ${\rm J}/\psi$ results (from the CMS experiment). In addition, the heavy-flavour $R_{\rm AA}$ and $v_2$ will be compared to results from Au-Au collisions at $\sqrt{s_{\rm NN}}=200~\mathrm{GeV}$ measured at RHIC. Finally, the heavy-flavour measurements will be compared to theoretical models.

Speaker:
Andrea Festanti
(Universita e INFN (IT))

Slides

12:00

Open charmed hadron production in p+p, Au+Au and U+U collisions at STAR20m

Heavy quarks are dominantly produced from initial hard scatterings in high-energy heavy ion collisions, and their interaction with QCD medium is sensitive to the medium dynamics. Thus heavy quarks are suggested as excellent probes to study the properties of the hot and dense nuclear matter created at the Relativistic Heavy Ion Collider. In this talk, we present the first results of open charm meson production in U+U collisions at $\sqrt{s_{NN}}$=193 GeV from the STAR experiment. We also report on updated results in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV, and those in p+p collisions at $\sqrt{s}$=200 GeV and 500 GeV. In these measurements, $D^{0}$ and $D^{*}$ mesons are reconstructed through hadronic decay channels. For both U+U and Au+Au collisions, invariant $D^{0}$ meson production yields are determined from minbias and 0-10$\%$ central triggered events for the $p_{T}$ range from 0 to 6 GeV/c. For p+p collisions, events with high $E_{T}$ triggers are used to extend the $p_{T}$ range of the measured cross section up to 10 GeV/c at $\sqrt{s}$=200 GeV and to 18 GeV/c at $\sqrt{s}$=500 GeV, respectively. Nuclear modification factors ($R_{AA}$) of open charm mesons are extracted from these results and are compared to various theoretical model calculations.

Speaker:
Prof.Zhenyu Ye
(University of Illinois at Chicago)

Slides

12:20

Measurement of single electrons from heavy flavor decays from $p$$+$$p$, $d$$+$Au, and Cu$+$Cu collisions in the PHENIX experiment20m

Charm and bottom quarks are formed predominantly by gluon fusion in
the initial hard scatterings at RHIC, making them good probes of the
full medium evolution. Previous measurements at RHIC have shown large
suppression and azimuthal anisotopy of open heavy flavor hadrons in
Au$+$Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Explaining the
simultaneously large suppression and flow of heavy quarks has been a
challenge for the community. To further understand the heavy flavor
transport in the hot medium, it is imperative to also measure cold
nuclear matter effects which affect the initial distribution of heavy
quarks as well as the system size dependence of the final state
suppression. In this talk, new measurements by the PHENIX collaboration of
single electrons from heavy flavor decays in $p$$+$$p$, $d$$+$Au, and
Cu$+$Cu collisions at $\sqrt{s_{NN}} = 200$ GeV are presented.
In particular, surprising enhancement of intermediate transverse momentum
heavy flavor leptons in d$+$Au at mid and backward rapidity are seen to grow
going to mid-central Cu$+$Cu collisions. This enhancement is much larger
than anti-shadowing of the parton distributions and is theoretically unexplained.

The main purpose of ALICE at the LHC is to investigate the properties of the deconfined state of strongly-interacting matter produced in high-energy heavy-ion collisions. Since heavy quarks, i.e. charm and beauty, are produced on a shorter time scale with respect to the hot fireball, they are suited to probe the interaction dynamics inside the medium.
The ALICE collaboration has measured the production of open heavy-flavour hadrons via their hadronic and semi-electronic decays at mid-rapidity and via the semi-muonic decay channel at forward rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV. The azimuthal distribution of heavy-flavour hadrons reflects the initial spatial anisotropy of the heavy-ion collision in case of sufficient re-scattering of the heavy quarks in the hot and dense matter. Therefore the heavy-flavour elliptic flow, the second harmonic in the Fourier expansion of the particle azimuthal distribution, is an observable sensitive to the degree of thermalization of charm and beauty quarks in the medium at low $p_{\rm T}$, as well as to the path length dependence of the energy loss of heavy quarks at high $p_{\rm T}$.
The elliptic flow measurements are presented for prompt charm mesons, i.e D$^{0}$, D$^{+}$, D$^{*+}$, and heavy-flavour decay electrons at mid-rapidity, as well as for heavy-flavour decay muons at forward rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV for various centrality intervals. The results will be compared with corresponding measurements of other hadron species. Results of the D-meson nuclear modification factor measured in the direction of the reaction plane and orthogonal to it will be also shown. Comparisons with model calculations will be discussed.

Speaker:
Raphaelle Bailhache
(Johann-Wolfgang-Goethe Univ. (DE))

Slides

11:00
→
13:00

Initial state physics: 1titanium

titanium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Carlos Pajares
(University Santiago de Compostela)

slides

11:00

The ridge through Colored Glass20m

The ridge in pp, p/d+A and A+A collisions manifest at very high multiplicities. Regardless of whether initial state or final state effects dominate, the physics of very high parton densities is relevant. In this talk, we attempt a synthesis of the state-of-the art in the CGC approach to computing both initial state and final state effects that generate collimated long range rapidity correlations. The emphasis throughout will be on a) quantitative comparisons to data, and b) on open problems in the different approaches that become manifest through such comparisons. We will discuss future measurements that are likely to provide definitive answers regarding the physics underlying this remarkable phenomenon.
References:
1) K. Dusling and R. Venugopalan, ``Initial state triangular azimuthal anisotropy in p+A and A+A collisions",in preparation.
2) B. Schenke, P. Tribedy, and R. Venugopalan, ``Multiplicity constrained v_n moments in pA and AA collisions in the IP-Glasma model", in preparation.
3) B.~ Schenke, P. Tribedy and R. Venugopalan,
``Multiplicity distributions in p+p, p+A and A+A collisions from Yang-Mills dynamics,'' Phys.\ Rev.\ C {\bf 89}, 024901 (2014).
4)A. Bzdak, B. Schenke, P. Tribedy and R. Venugopalan,``Initial state geometry and the role of hydrodynamics in proton-proton, proton-nucleus and deuteron-nucleus collisions,''Phys.\ Rev.\ C {\bf 87}, 064906 (2013).

Speaker:
Raju Venugopalan

Slides

11:20

Higher harmonics from intrinsic multi-particle production20m

We explore the detailed structure of the {\em ridge} in the Color-Glass-Condensate (CGC) effective field theory of QCD and demonstrate a novel mechanism that produces a non-vanishing $v_3$ without final-state re-scattering. A $v_3$ in agreement with the LHC p+Pb data is generated by the interference of diagrams attributed to the jet (away-side) and ridge (near-side) substructure of the azimuthal correlation. We also find that the $v_3$ in p+A is comparable to that in A+A for similar multiplicities.

Speaker:
Kevin Dusling

Slides

11:40

Initial state geometry and fluctuations in deformed and asymmetric nuclear collisions in the IP-Glasma framework20m

The IP-Glasma model of initial conditions based on the *ab initio* color glass condensate (CGC) framework successfully explains the bulk features of global data for various systems like p+p, p+A and A+A over a wide range of energies [1-3]. We employ this framework to study deformed U+U collisions, asymmetric Cu+Au collisions and the effect of deformation in Au+Au collisions at RHIC. A combined study of these heavy ion systems with varying initial geometries can provide a unique opportunity to determine the origin of different sources of fluctuations that affect global observables like multiplicity and flow. We study the sensitivity of multiplicity, eccentricity and their event-by-event distributions to the details of initial state geometry. Results are compared to a two component MC-Glauber model implementation that includes Negative-Binomial multiplicity fluctuations. We argue that measurements of global observables for these systems at RHIC can constrain the mechanism of multi-particle production [4].
Ref :
[1]B .Schenke, P. Tribedy, R. Venugopalan, Phys. Rev. Lett. 108 (2012) 252301, Phys.Rev. C89 (2014) 024901.
[2]C. Gale, S. Jeon, B. Schenke, P. Tribedy, R. Venugopalan, Phys.Rev.Lett. 110 (2013) 012302.
[3]A. Bzdak, B. Schenke, P. Tribedy, R. Venugopalan, Phys. Rev. C 87, 064906 (2013).
[4]B .Schenke, P. Tribedy, R. Venugopalan *in preparation*

Speaker:
Prithwish Tribedy
(VECC)

Slides

12:00

Flow measurements and selection of body-body and tip-tip enhanced samples in U+U collisions at STAR20m

The azimuthal anisotropy of particle production is commonly used in high-energy nuclear collisions to study the early evolution of the expanding system. The prolate shape of uranium nuclei provides the possibility to study how the initial geometry of the nuclei affects the azimuthal distributions. It also provides a unique opportunity to understand the initial conditions for particle production at mid-rapidity in heavy ion collisions.
In this talk, the two- and four- particle cumulant, $v_2$($v_2{2}$ and $v_2{4}$), from U+U collisions at $\sqrt{s_{NN}}=$ 193 GeV and Au+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV for inclusive charged hadrons will be presented. The STAR Zero Degree Calorimeter is used to subdivide the 0-1% centrality bin into even finer centralities. Differences were observed between the multiplicity dependence of $v_2{2}$ for most central Au+Au and U+U collisions. Data was compared with a Monte Carlo Glauber model and it was seen that this model cannot explain the multiplicity dependence of $v_2{2}$ in central collisions. It has also been demonstrated that ZDC and multiplicity in combination provide a way to select body-body or tip-tip enhanced samples of central U+U collisions. We will also present preliminary $v_1$ and $v_2$ results for inclusive charged hadrons from Au+Au and U+U collisions, with the first-order event plane determining from spectator neutrons. This type of event plane represents the reaction plane instead of the participant plane as used in other methods, this analysis provides an alternative approach to examine the eccentricity-scaling to reveal the QGP properties.

Speaker:
Hui Wang
(Brookhaven National Lab)

Slides

12:20

Photonuclear production of vector mesons in ultra-peripheral Pb-Pb collisions at the LHC20m

Vector mesons are copiously produced in ultra-peripheral
nucleus-nucleus collisions. In these collisions, the nuclei are
separated by impact parameters larger than the sum of the nuclear
radii, and the interaction is mediated by the electromagnetic
field. The interaction effectively corresponds to a photonuclear
interaction between a photon, generated from the electromagnetic field
of one of the nuclei, and the target nucleus. The ALICE Collaboration
has previously published results on exclusive J/$\psi$ photoproduction
at mid and forward rapidities in Pb-Pb collisions. The cross section
for this process is a particularly good measure of the nuclear gluon
distribution. In this talk, the latest results on exclusive production
of light and heavy vector mesons from ALICE in Pb-Pb collisions will
be presented.

Speaker:
Joakim Nystrand
(University of Bergen (NO))

Slides

12:40

Double-parton scatterings in proton-nucleus and nucleus-nucleus collisions at the LHC20m

We have derived a simple generic expression to compute the cross sections for double-parton scatterings
(DPS) in high-energy proton-nucleus and nucleus-nucleus collisions as a function of the
corresponding single-parton hard cross sections [1,2]. Estimates of DPS contributions at LHC energies for
(i) same-sign W-boson pair production in p-Pb, and (ii) double-J/$\psi$ production in Pb-Pb, are
obtained from NLO predictions with nuclear PDF modifications for the corresponding single-parton
scatterings. The first process can help determine the effective $\sigma_{\rm eff}$ parameter characterising
the transverse distribution of partons in the nucleon, whereas the second one provides interesting
insights on the event-by-event dynamics of J/$\psi$ production in Pb-Pb. The expected cross sections
and event rates after typical acceptance and efficiency losses, for various others DPS processes involving
quarkonia, jets, and gauge bosons ($\gamma$, W, Z) will be given for p-Pb and Pb-Pb collisions at the LHC.
[1] D. d'Enterria, A. Snigirev, Phys.Lett. B718 (2013) 1395
[2] D. d'Enterria, A. Snigirev, Phys.Lett. B727 (2013) 157

Speaker:
David d'Enterria
(CERN)

Slides

13:00
→
14:20

Lunch
1h 20m

14:20
→
16:00

Approach to equilibriumtitanium

titanium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Urs Wiedemann
(CERN)

14:20

Early isotropization of the quark-gluon plasma20m

In recent years, the problem of thermalization in Heavy Ion Collision has received much attention, but has yet to be solved.
The issue is the following: on one hand, viscous hydrodynamics simulations suggest that the matter produced in such collisions (called the Quark Gluon Plasma, or QGP) behaves like a nearly perfect fluid, and does so very shortly after the collision (around 1 fm/c). Since hydrodynamics has local thermal equilibrium in its prerequisites, this tends to show that the QGP has thermalized during the very early stages of the collision. On the other hand, theoretical models (based on microscopic theories like the Color Glass Condensate, or CGC) predict that the QGP is very far from local thermal equilibrium at the initial time (among other non-thermal features, its energy-momentum tensor is very anisotropic).
One of the approaches developed to study this non-perturbative problem in QCD is a resummation scheme that amounts to averaging over classical fields, with random initial conditions given by a one loop calculation in the CGC framework.
We present here the results that we obtained by following this approach – the so-called classical statistical approximation or CSA, showing an early isotropization of the system compatible with viscous hydrodynamics. As a final remark, some recently found theoretical limitations of the CSA will be briefly mentioned.

Speaker:
Thomas Epelbaum
(IPhT)

Slides

14:40

Equilibration of anisotropic quark-gluon plasma produced by decays of color flux tubes20m

A set of kinetic equations is used to study equilibration of the anisotropic quark-gluon plasma produced by decays of color flux tubes possibly created at the very early stages of ultra-relativistic heavy-ion collisions. The decay rates of the initial color fields are given by the Schwinger formula, and the collision terms are treated in the relaxation-time approximation. By connecting the relaxation time with viscosity we are able to study production and thermalization processes in the plasma characterized by different values of the ratio of the shear viscosity to entropy density, ${\bar \eta}$. For the lowest (KSS) value of this ratio, $4\pi{\bar \eta} = 1$, and realistic initial conditions for the fields, the system approaches the viscous-hydrodynamics regime within 1--2 fm/c. On the other hand, for larger values of the viscosity, $4\pi{\bar \eta} \geq 3$, the collisions in the plasma become inefficient to destroy collective phenomena which manifest themselves as oscillations of different plasma parameters. The presence of such oscillations brings in differences between the kinetic and hydrodynamic descriptions, which suggest that the viscous-hydrodynamics approach after 1--2 fm/c is not complete if $4\pi{\bar \eta} \geq 3$ and should be extended to include dissipative phenomena connected with color conductivity.
Presentation based on the article published as Phys. Rev. D88 (2013) 034028

When and to what extent a thermalized Quark Gluon Plasma is achieved in heavy-ion collision impacts the quantitative extraction of transport properties in the QGP. We address this problem by employing the largest to date real time classical-statistical lattice simulations. Most remarkably, we find that the thermalization process is governed by a universal attractor, where the space-time evolution of the plasma becomes independent of the initial conditions [1,2]. In this classical regime, the plasma exhibits the self-similar dynamics characteristic of wave turbulence, as observed in a large variety of strongly correlated many-body systems. We interpret the consequences of our numerical lattice results for thermalization in heavy-ion experiments.
[1] J.Berges,K.Boguslavski,S.Schlichting,R.Venugopalan; arXiv:1303.5650 [hep-ph].
[2] J.Berges,K.Boguslavski,S.Schlichting,R.Venugopalan; arXiv:1311.3005 [hep-ph].

Speaker:
DrSören Schlichting
(Brookhaven National Lab)

Slides

15:20

Structure of chromomagnetic fields in the glasma20m

The initial stage of a heavy ion collision is dominated by nonperturbatively strong chromoelectric and -magnetic fields. The properties of these fields can be calculated numerically using the CGC description of the small x degrees of freedom of the colliding nuclei. The spatial Wilson loop provides a gauge invariant observable to probe the dynamics of the longitudinal chromomagnetic field. This talk describes the results from a recent real time lattice calculation (arXiv:1401.4124) of the area-dependence of the expectation value of the spatial Wilson loop.
We consider ensembles of gauge field configurations generated from the MV-model classical Gaussian effective action as well as solutions of the JIMWLK high-energy renormalization group equation with fixed and running coupling. The initial fields exhibit domain-like structure over distance scales of the order of the saturation scale. At later times universal scaling emerges at large distances for all ensembles, with a nontrivial critical exponent. A similar behavior has earlier been seen in calculations of the gluon transverse momentum spectrum, which becomes independent of the initial spectrum of gauge fields (i.e. the initial unintegrated gluon distribution) for momenta less than the saturation scale. Finally, we compare the results for the Wilson loop to the two-point correlator of magnetic fields.

Speaker:
Tuomas Lappi
(University of Jyvaskyla)

Slides

15:40

Gluon transport equation in the small-angle approximation and the onset of Bose-Einstein condensation20m

To understand the evolution of a dense system of gluons, such as those produced in the early stages of ultra-relativistic heavy ion collisions, is an important and challenging problem. We describe the approach to thermal equilibrium using the small angle approximation for gluon scattering in a Boltzmann equation that includes the effects of Bose statistics. The role of Bose statistical factors in amplifying the rapid growth of the population of the soft modes is essential. With these factors properly taken into account, one finds that elastic scattering alone provides an efficient mechanism for populating soft modes, and in fact leads to rapid infrared local thermalization.
Furthermore recent developments suggest that high initial overpopulation plays a key role and may lead to dynamical Bose-Einstein Condensation. The kinetics of condensation is an interesting problem in itself. By solving the transport equation for initial conditions with a large enough initial phase-space density the equilibrium state contains a Bose condensate, and we present numerical evidence that such over-populated systems reach the onset of Bose-Einstein condensation in a finite time. It is also found that the approach to condensation is characterized by a scaling behavior. Finally we discuss a number of extensions of the present study.
Reference: Blaizot, Liao, McLerran, Nucl. Phys. A920(2013)58.

Speaker:
Jinfeng Liao
(Indiana University)

Slides

14:20
→
16:05

Collective dynamics: 2europium

europium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Laszlo Csernai
(Department of Physics and Technology)

announcement

14:20

Beam energy dependence of the viscous damping of anisotropic flow20m

The flow harmonics $v_{2,3}$ for charged hadrons, are studied for a broad range of centrality selections and beam collision energies in Au+Au ($\sqrt{s_{NN}}= 7.7 - 200$ GeV) and Pb+Pb ($\sqrt{s_{NN}}= 2.76$ TeV) collisions. They validate the characteristic signature expected for the system size dependence of viscous damping at each collision energy studied. The extracted viscous coefficients, that encode the magnitude of the ratio of shear viscosity to entropy density $\eta/s$, are observed to decrease to an apparent minimum as the collision energy is increased from $\sqrt{s_{NN}}= 7.7$ to approximately 62.4~GeV; thereafter, they show a slow
increase with $\sqrt{s_{NN}}$ up to 2.76 TeV. This pattern of viscous damping provides the first experimental constraint for $\eta/s$ in the temperature-baryon chemical potential ($T, \mu_B$) plane, and could be an initial indication for decay trajectories which lie close to the critical end point in the phase diagram for nuclear matter.

Speaker:
Roy Lacey
(Stony Brook University)

Slides

14:40

Elliptic flow of identifed particles in Pb-Pb collisions at the LHC20m

We report the measurements of elliptic flow for identified particles produced in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV with the ALICE detector at the LHC.
The second Fourier coefficient, $v_2$, measured with the scalar product method with a large pseudo-rapidity gap of $|\Delta\eta| > 2.0$, is reported for $\pi$, ${\rm K}^{\pm}$, ${\rm K}^0_s$, p ($\overline{\mathrm{p}}$), $\phi$, $\Lambda$ ($\overline{\mathrm{\Lambda}}$), $\Xi$ and $\Omega$.
We will present the transverse momentum $p_{\mathrm{T}}$ dependence of the $v_2$ of each particle for several centrality classes. In the low $p_{\mathrm{T}}$ region ($p_{\mathrm{T}} < 2$ GeV/$c$) our data are described fairly well by hydrodynamical calculations. We will discuss our results in the intermediate $p_{\mathrm{T}}$ region $2 < p_{\mathrm{T}} < 5$ GeV/$c$, where the scaling with the number of constituent quarks was first reported at RHIC energies.

Speaker:
Alexandru Florin Dobrin
(University of Utrecht (NL))

Slides

15:00

Elliptic flow of light nuclei and identified hadrons, their centrality and energy dependence in STAR20m

A strongly interacting medium, namely Quark Gluon Plasma (QGP), is formed in high energy heavy ion collisions at RHIC. Elliptic flow $(v_{2})$, the second order Fourier coefficient of azimuthal distribution of the produced particles with respect to reaction plane, is used to investigate the properties of QGP. Light nuclei ($d$, $\bar{d}$, $t$, $^{\small{3}}He$), produced in such collisions, are believed to be formed by coalescence of nucleons. By comparing $v_{2}$ of light nuclei with their constituents, we can understand the production mechanism of nuclei in heavy ion collisions. At top RHIC energies, identified hadron $v_{2}$ revealed many features like the number-of-constituent quark (NCQ) scaling and mass ordering. With the combined statistics, we can test the scaling behaviors for rare multi-strange particles ($\phi$, $\Xi $ and $\Omega$). An energy dependent difference in $v_{2}$ ($\Delta v_{2}$) between particles and anti-particles was also observed in beam energy scan data at STAR.
In this talk, we show the $p_{T}$ and centrality dependence of $v_{2}$ of light nuclei ($d$, $\bar{d}$, $t$, $^{3}He$), and identified hadrons ($\pi^{\pm}$, $K^{\pm}$, $K_{s}^{0}$, $p$, $\bar{p}$, $\phi$, $\Lambda$, $\bar{\Lambda}$, $\Xi^{\pm}$, $\Omega^{\pm}$) at mid-rapidity for Au+Au collisions at $\sqrt{s_{NN}}\ =\ 7.7,\ 11.5,\ 19.6,\ 27,\ 39,\ 62.4$ and $200$ GeV from STAR. Light nuclei and hadrons are identified using the time projection chamber and time-of-flight detector systems of STAR. The mass number and constituent quark scaling of nuclei $v_{2}$ will be presented. Light nuclei $v_{2}$ will be compared to those from $p$($\bar{p}$) and to a coalescence model calculation using the phase space distributions of produced nucleons in a transport model. The centrality dependence of $\Delta v_{2}$ for identified hadron will be shown and compared to model calculations.
We further discuss NCQ scaling and mass ordering of multi-strange hadron $v_{2}$ at the top energy Au+Au collisions at RHIC.

The collective expansion in relativistic heavy-ion collisions is initially highly anisotropic. Due to viscosity, this leads to strongly deformed local momentum distributions which invalidates the standard viscous hydrodynamic expansion around a local equilibrium distribution, causing a breakdown of viscous fluid dynamics à la Israel and Stewart at early times. We have developed an improved formulation of viscous hydrodynamics [1] that is based on an expansion around a spheroidally deformed local momentum distribution. A spheroidal local momentum distribution leads to the "anisotropic hydrodynamics" developed earlier by Martinez and Strickland, which accounts non-perturbatively for the resulting large early-time anisotropy between the longitudinal and transverse pressures. By allowing in our new treatment for additional small deviations of the local momentum distribution from spheroidal symmetry, we arrive at a complete formulation of second-order viscous hydrodynamics in which the large longitudinal-transverse momentum anisotropy is treated non-perturbatively à la Martinez and Strickland while the smaller remaining viscous stress components are treated perturbatively à la Israel and Stewart. We perform a test of the approach for a system undergoing boost-invariant longitudinal expansion without transverse expansion which maximizes the longitudinal-transverse pressure anisotropy. For this system the Boltzmann equation can be solved exactly in the relaxation-time approximation, allowing for a quantitative test of effective macroscopic hydrodynamic theories. We find that the viscous anisotropic hydrodynamic framework ("vaHydro") significantly outperforms all other available hydrodynamic descriptions, for both small and large values of the shear viscosity $\eta/s$. We expect vaHydro to provide a superior description also after including transverse expansion and to allow for an earlier matching of pre-equilibrium dynamics to hydrodynamics, due to the superior ability of vaHydro to handle the large differences in longitudinal and transverse expansion rates at early times.
[1] D. Bazow, U. Heinz, M. Strickland, arXiv:1311.6720, Phys. Rev. C, in press.

Speaker:
Ulrich Heinz
(The Ohio State University)

Slides

15:40

Extracting the bulk viscosity of the quark-gluon plasma25m

Currently, most fluid-dynamical simulations of relativistic heavy ion collisions take into account only dissipative effects originating from shear viscosity. However, there is no a priori reason to neglect bulk viscosity since the actual order of magnitude and temperature dependence of this transport coefficient is unknown, and could be significant. In this work, we explore the phenomenological implications of a nonzero bulk viscosity coefficient on transverse momentum spectra and azimuthal momentum anisotropy. We then extract the optimal values of the bulk and shear viscosity coefficients that are able to describe these observables. For ultracentral heavy ion collisions, measured by ATLAS and CMS, we perform this analysis using several initial condition models. For other centrality classes, we determine these coefficients using the IP-Glasma initial condition model. Our fluid-dynamical description is the most complete available and includes all possible second order terms that appear in Israel-Stewart theory, including those that couple bulk viscous pressure to shear stress. The transport coefficients of all terms are computed using kinetic theory. We find that the optimum values of shear viscosity extracted from data can be modified up to 50% when bulk viscosity is included.
We further discuss the effects of baryon chemical potential on the shear viscosity of bulk nuclear matter. We show that a hadron resonance gas with large baryon number density is closer to the ideal fluid limit than the corresponding gas with zero baryon number.

Speaker:
DrGabriel Denicol
(McGill University)

Slides

14:20
→
16:00

Electromagnetic probes: 2helium

helium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Thomas Peitzmann
(University of Utrecht (NL))

slides

14:20

Centrality dependence of soft photon production and its collective flow in Au$+$Au collisions at $\sqrt{s_{NN}} = 200$ GeV20m

Soft photons are of particular interest since they are unmodified once
produced, and thus carry information about the space-time thermal
properties of the medium. We present new results on the centrality
dependence of soft single photons in Au$+$Au collisions, down to $p_T
= 400$ MeV/$c$ via photon conversions to $e^+e^-$ pairs. These
measurements provide stringent tests of the hydrodynamic space-time
evolution as a detailed function of the collision geometry.
These soft photons have different angular emission patterns depending
on their production mechanism. Previous published PHENIX results
indicate that the second order Fourier coefficient ($v_2$) is postive
for $p_T < 4$ GeV/$c$, which is qualitatively explained by
hydrodynamical model calculations, but not quantitatively. The
3\textsuperscript{rd} order Fourier coefficient ($v_3$) of photons has
been proposed as a critical additional handle to understand the photon
emission. Photons emitted under the presence of strong magnetic field
created in the collision would have a significant influence on $v_2$
while very little on $v_3$. In contrast, hydrodynamical models
predict a sizable photon $v_3$. We report the latest results on the
centrality dependence of the soft photon production and the $v_2$ and
$v_3$ coefficients in Au$+$Au collisions at $\sqrt{s_{NN}} = 200$ GeV.

One important physics goal of ultra-relativistic heavy-ion collisions is
to study the fundamental properties of a hot, dense medium created in these collisions.
This medium is expected to emit thermal radiation which is in the
form of direct photons and dileptons. Once produced, photons and leptons
traverse the strongly interacting medium with minimal interactions.
The fully installed Time-of-Flight Detector in 2010 enables clean electron
identification from low to intermediate transverse momentum ($p_{T}$). In this
talk, we will present the direct virtual photon production for 1<$p_{T}$<5 GeV/$c$
derived from the dielectron continuum in the dielectron invariant mass region 0.1<$M_{ee}$<0.3 GeV/$c^{2}$
from one billion $\sqrt{s_{NN}}$ = 200 GeV Au+Au minimum bias events taken in 2010 and 2011.
In addition, we will present the centrality and $p_{T}$ dependence of dielectron production
and the dielectron azimuthal angle correlation in the intermediate mass(1.1<$M_{ee}$<3 GeV/$c^{2}$) region in this dataset.
The relevant results from $\sqrt{s}$ = 200 GeV p+p collisions taken in 2012 will also be discussed.
Comparisons to model calculations including hadronic and partonic thermal radiation will be made for
both the direct virtual photon and dielectron production in Au+Au collisions.

Speaker:
Chi Yang
(USTC/BNL)

Slides

15:00

Direct-photon spectra and flow in Pb-Pb collisions at the LHC measured with the ALICE experiment20m

Unlike hadrons, direct photons are produced in all stages of a
nucleus-nucleus collision and therefore test our understanding of the
space-time evolution of the produced medium. Of particular interest
are
so-called thermal photons expected to be produced in a quark-gluon
plasma and the subsequent hadron gas.
The transverse momentum spectrum
of thermal photons carries information about the temperature of the
emitting medium. The effect of Doppler blueshift on photons spectra
from later and colder stages of a
collision, however, potentially
complicates the extraction of the temperature.
In this presentation,
direct-photon spectra in the range $1 < p_T < 12$ GeV/c from Pb-Pb
collisions at
$\sqrt{s_{NN}} = 2.76$ TeV will be shown. The results
were obtained with two independent methods:
by measuring photons with
the electromagnetic calorimeter PHOS and by measuring $e^+e^-$ pairs
from
external conversions of photons in the detector material. The
measured direct-photon spectra will be
compared with predictions from
state-of-the-art hydrodynamic models. In addition, direct-photon
production
in p-Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV will be
discussed. In the standard hydrodynamical
modeling of nucleus-nucleus
collisions, thermal photons mostly come from the early hot stage of the
collision. As collective hydrodynamic flow needs time to build up, the
azimuthal anisotropy of
thermal photons quantified with Fourier
coefficient $v_2$ is expected to be smaller than the one for
hadrons. However, the PHENIX experiment and ALICE experiment observed
$v_2$ values of direct-photons
similar in magnitude to the pion
$v_2$. These unexpected observations constitute the so called
"direct-photon flow puzzle" as they challenge the standard
hydrodynamic picture of nucleus-nucleus
collisions and/or the standard
photon emissions rates in the quark-gluon plasma and the hadron
gas.
We will present the inclusive photon $v_2$ and $v_3$ in Pb-Pb
collisions at $\sqrt{s_{NN}} = 2.76$
TeV in the range $1 < p_T < 5$
GeV/c and discuss implications for the $v_2$ and $v_3$ of
direct-photons.

A relatively small spectral slope and large elliptic flow of direct photons
measured at RHIC and LHC has reignited the discussion of thermal photons as a
probe of the quark-gluon plasma (QGP). We present a systematic discussion of the
macro- and micro-physics that figures into calculating thermal emission spectra.
For the bulk medium we compare the temperature and flow evolution in fireball [1]
and hydrodynamic approaches [2], and study how different tunes of initial
conditions, compatible with bulk hadron observables, affect the photon spectra.
We deduce evidence for an enhancement of currently available hadronic and QGP
emission rates around Tc, and a potential suppression of early QGP radiation
(indicative for a gluon-rich early QGP). We then present an updated (more complete)
assessment of hadronic emission channels involving meson exchange reactions in
baryon-meson scattering which have not been considered thus far [3]. We also
investigate consequences for thermal dilepton v2.
[1] H. van Hees, C. Gale and R. Rapp, Phys. Rev. C 84 (2011) 054906
[2] H. van Hees, M. He and R. Rapp, in preparation.
[3] N. Holt and R. Rapp, work in progress.

Speaker:
Prof.Ralf Rapp
(Texas A&M University)

Slides

15:40

Probing the non-equilibrium dynamics of hot and dense QCD with dileptons20m

Much work has been devoted to the determination of an effective value of the shear viscosity coefficient from analyses of the hadronic final states in relativistic heavy-ion collisions. Electromagnetic radiation, however, constitutes a class of complementary and penetrating probes that are sensitive to the entire space-time history of nuclear collisions including its very early stages. We show that thermal dileptons (and photons) are affected by the transport properties of the fluid and by the non-equilibrium aspects of the initial state that are usually inaccessible to hadronic probes. For the first time, we explicitly demonstrate that electromagnetic spectra and azimuthal momentum anisotropy can be used not only to investigate the magnitude of the shear relaxation time and to differentiate between possible initial shear-stress tensors, but also to reveal the temperature dependence of the shear viscosity coefficient. We further show that the dependence of electromagnetic probes on these quantities comes mostly from processes occurring in the QGP phase. Our approach utilizes event-by-event 3+1D viscous hydrodynamic simulations (MUSIC) [1], and the dilepton emission sources include contributions from charm decay and hadronic rates extracted from in-medium spectral functions [2].
[1] Bjoern Schenke, Sangyong Jeon, Charles Gale, Phys.Rev. C82 (2010) 014903
[2] Gojko Vujanovic, Clint Young, Bjoern Schenke, Ralf Rapp, Sangyong Jeon, and Charles Gale, arXiv:1312.0676, PRC in press.

Speaker:
Gojko Vujanovic
(McGill University)

Slides

14:20
→
16:00

Heavy flavor: 2platinum

platinum

darmstadtium

The full space-time evolution of heavy quarks and light partons in ultra-relativistic heavy-ion collisions is studied within the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS). We discuss in detail for all flavors the influence of elastic and radiative energy loss with a running coupling. Radiative processes, in particular, are implemented through an improved version of the Gunion-Bertsch matrix element, which is derived from comparisons to the exact result. In this calculation the finite heavy quark masses are explicitly taken into account, leading to the dead cone effect. Consequently, we present results of this updated version of BAMPS and compare them to experimental data at RHIC and LHC. In detail, the nuclear modification factor and elliptic flow of charged hadrons, heavy flavor electrons as well as muons, D mesons, and non-prompt J/psi are discussed. The latter two are especially sensitive to the mass difference of charm and bottom quarks. Furthermore, we make predictions where no data is available yet.

Speaker:
Jan Uphoff
(Goethe University Frankfurt)

Slides

14:40

AdS/CFT heavy-quark energy loss beyond the leading order20m

We present new predictions for the suppression of heavy quark decay products at RHIC and LHC from a NLO AdS/CFT energy loss model. Previous predictions from a tomographic model based on only the leading order AdS/CFT contribution to energy loss and constrained by RHIC data disagreed with LHC D meson measurements. In this work we include for the first time a correct treatment of the momentum fluctuations induced in the heavy quark motion from the strongly-coupled thermal medium: we resolve the ambiguity in the evaluation of the stochastic Langevin equations using the Wong-Zakai theorem and properly take into account the fluctuations' deviations from the Einstein relations. The addition of the fluctuations leads to corrections to the suppression predictions, which are significant for charm quarks and their decay products. We demonstrate how further experimental measurements can provide insight into the dominant energy loss mechanisms in, and hence the physical properties of, the quark-gluon plasma produced in heavy ion collisions.

Speaker:
William Horowitz
(University of Cape Town)

Slides

15:00

Measurements of the heavy-flavour nuclear modification factor in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE at the LHC20m

The LHC heavy-ion physics program aims at investigating the properties
of strongly interacting matter at extreme conditions of temperature and
energy density, where the formation of the Quark-Gluon Plasma (QGP) is
expected.
In high-energy heavy-ion collisions, heavy quarks are regarded as
effective probes of the properties of the QGP as they are created on a
short time scale, with respect to that of the QGP, and
subsequently interact with it.
The nuclear modification factor $R_{\rm AA}$, defined as the ratio of
the yield measured in
Pb-Pb to that observed in pp collisions scaled with the number of binary
nucleon-nucleon collisions, is used to study the mechanisms of
heavy quark in-medium energy loss and hadronization.
In order to disantangle hot and cold nuclear matter effects, the nuclear
modification factor was measured in p-Pb collisions where the
formation of a large volume hot and dense medium is not expected.
Heavy-flavour production in p-Pb collisions has also its own interest
since it allows us to investigate initial state effects such as
modifications of the parton distribution functions in the nucleus, gluon
saturation and $k_{\rm T}$ broadening.
With ALICE, the detector designed and optimized for heavy-ion physics
at the LHC, open heavy flavours are measured at central rapidity
using using their hadronic and semi-electronic decays as
well as at forward and backward rapidity using their semi-muonic decays.
The latest results on the nuclear modification factor of charmed mesons and
electrons and muons from heavy-flavour hadron decays in p-Pb collisions
at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be presented.
Comparisons with theoretical predictions will be discussed.

Speaker:
Shuang Li
(Univ. Blaise Pascal Clermont-Fe. II (FR))

Slides

15:20

Heavy-flavour production as a function of multiplicity in pp and p-Pb collisions20m

The measurement of heavy-flavour production cross sections in pp collisions at the LHC provides a reference for heavy-ion studies and represents a test for perturbative QCD calculations. In p-Pb collisions, heavy-flavour measurements are essential to assess the effects due to the presence of a nucleus in the initial state, such as the modification of the parton densities and the $k_{\rm T}$-broadening resulting from multiple soft scatterings of the partons.
Heavy-flavour measurements as a function of the
multiplicity of charged particles produced in the collision are sensitive to
the interplay between hard and soft contributions to particle production and,
in particular, could give insight into the role of multi-parton interactions
(MPI), i.e. several hard partonic interactions occuring in a single collision
at high centre-of-mass energies.
In this talk we will focus on the measurement of open heavy-flavour production as a function of charged-particle multiplicity in pp collisions at $\sqrt {s}$ = 7 TeV and p-Pb collisions at $\sqrt {s_{\rm NN}}$=5.02 TeV recorded with the ALICE detector in 2010 and 2013, respectively. D$^{0}$, D$^{+}$ and D$^{*+}$ are reconstructed from their hadronic decay modes in the central rapidity region, and their yields are measured in different multiplicity and $p_{\rm T}$ intervals.
The per-event yield of D mesons in the different multiplicity intervals, normalized to its multiplicity-integrated value, and its evolution with $p_{\rm T}$ will be compared for pp and p-Pb collisions to study the contribution of MPI to open charm production in the two systems.
The nuclear modification factor of D mesons in p-Pb collisions, defined as the ratio of the D-meson yield in p-Pb and pp collisions scaled by the number of binary collisions $N_{\rm coll}$, will be discussed in terms of its multiplicity dependence.
Results obtained with different multiplicity estimators will be shown in order to better understand the connection between multiplicity and collision geometry, which is needed to determine $N_{\rm coll}$.

Speaker:
Riccardo Russo
(Universita e INFN (IT))

Slides

15:40

Open beauty measurements in pPb collisions with CMS20m

We report the first measurements of fully reconstructed B mesons in collisions involving heavy ions. Rapidity and transverse momentum cross sections, measured at $\sqrt{s_{NN}}=5.02$ TeV with the CMS detector, will be presented. For the same collision system, we will also report on the production of inclusive $b$-hadrons identified via their decays into $J/\psi$ displaced from the primary collision vertex, and measured in a similar kinematic range as the identified B mesons. The nuclear modification factors, which are constructed using a theoretically calculated pp reference, will be shown together with cross-section asymmetries between equivalent positive and negative pseudo-rapidity ranges in the center-of-mass frame of the collision.

Speaker:
Hyunchul Kim
(Korea University (KR))

Slides

16:05
→
16:30

Coffee break
25m

16:30
→
18:30

Collective dynamics: 3europium

europium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Barbara Erazmus
(CNRS/IN2P3)

announcement

16:30

Searches for azimuthal flow in pp, p-Pb and Pb-Pb collisions from ALICE20m

A key question facing the heavy-ion physics community is whether or not collective behavior develops in elementary collisions. We will utilize a variety of techniques designed to obtain elliptic and triangular flow coefficients ($v_{2}$ and $v_{3}$) on data from pp $\sqrt{s} = 7$ TeV and p-Pb $\sqrt{s_{\rm NN}} = 5.02$ TeV collisions. We will report new measurements of second, fourth, and sixth particle flow cumulants for charged hadrons in p-Pb collisions as a function of charged hadron multiplicity, and discuss their response to few and global azimuthal correlations. New results will also be shown for Pb-Pb $\sqrt{s_{\rm NN}} = 2.76$ TeV, as they provide a crucial reference for such studies. Finally, we will report new measurements of $v_{2}\{SP\}$ for charged hadrons and identified particles for pp and p-Pb collisions. Investigations into mass ordering and comparisons to measurements of $v_{2}\{SP\}$ from Pb-Pb collisions will be carried out.

Speaker:
Anthony Robert Timmins
(University of Houston (US))

Slides

16:50

A scaling relation between proton-nucleus and nucleus-nucleus collisions20m

I compare the flow-like correlations in high multiplicity proton-nucleus (p + A) and nucleus- nucleus (A + A) collisions. At fixed multiplicity, the correlations in these two colliding systems are strikingly similar, although though the system size in p + A is smaller. Based on an independent cluster model and a simple conformal scaling argument, where the ratio of the mean free path to the system size stays constant at fixed multiplicity, I argue that flow in p + A emerges as a collective response to the fluctuations in the position of the clusters, just like in A + A collisions. By examining the recent LHC data carefully, I show that this simple model captures the essential physics of elliptic and triangular flow in p + A collisions. I also explore the implications of the model for jet energy loss in p + A collisions.

Speaker:
DrGokce Basar
(Stony Brook University)

Slides

17:10

Flow in Cu+Au collisions and unique tests of 3D medium evolution20m

Cu$+$Au collisions at RHIC have provided the first asymmetric
heavy-ion collisions at collider energies, where it is generally
believed that nuclear matter above the Quark-Gluon Plasma (QGP) transition is created. The
Cu$+$Au system provides a unique arena for QGP production and
development with novel features that are inaccessible in symmetric
A$+$A collisions, such as intrinsic transverse triangularity at
mid-centrality and a completely occluded, corona-less smaller nucleus
in the most central collisions. Further, because the participant
nucleon groups from the two nuclei are distinguishably different it
may be possible to trace the sources of initial deposition of such
conserved quantities as energy and transverse momentum in 3D across
the medium. In this talk we present new PHENIX results on flow
observables from Cu$+$Au collisions across both $p_T$ and
(pseudo)rapidity, and discuss how they can be used to diagnose the full three-dimensional
formation and evolution of the QGP fluid.

An updated version of the partonic transport model Boltzmann Approach to Multi-Parton Scatterings (BAMPS) is presented, which numerically solves the 3+1D Boltzmann equation by allowing interactions among all parton species: gluons, light quarks, and heavy quarks with both elastic and inelastic collisions. We introduce the improved Gunion-Bertsch matrix element, which cures problems of the original Gunion-Bertsch result in characteristic regions of the phase space. Based on extensive numerical calculations, the improved matrix element agrees well with the exact pQCD calculation. While employing the new matrix element, important properties of the quark-gluon plasma created in heavy-ion collisions such as the thermalization time of the plasma and the shear viscosity over entropy density ratio are calculated within the microscopic transport model BAMPS. Furthermore, we compare our results of the nuclear modification factor and elliptic flow to experimental data measured at RHIC and LHC.

Recent results in d+Au and p+Pb collisions at RHIC and the LHC provide evidence for collective expansion and flow of the created medium. We propose a control set of experiments to directly compare particle emission patterns from p+Au, d+Au, and He3+Au or t+Au collisions at the same sqrt(sNN). Using Monte Carlo Glauber we find that a He3 or triton projectile, with a realistic wavefunction description, induces a significant intrinsic triangular shape to the initial medium and that, even with viscous damping, this survives into a significant third order flow moment v3. By comparing systems with one, two, and three initial hot spots, one can disentangle the effects from the initial spatial distribution of the deposited energy and viscous damping. These are key tools to answering the question of how small a droplet of matter is necessary to form a quark-gluon plasma described by nearly inviscid hydrodynamics. We describe our results from (arXiv:1312.4565) as well as new calculations including coupling to a hadronic cascade afterburner and full particle identified flow patterns.

Speaker:
Paul Romatschke
(U)

Slides

18:10

Will perfect fluidity of the sQGP survive in light of the BES & D+Au & p+Au data?20m

Recent low pT<2 GeV vn data on the beam energy scan (BES) and D+Au at RHIC and the surprising data on low pT vn in p+Pb at LHC challenge long held assumptions about the validity or necessity of perfect fluid hydrodynamics in A+A. Could classical field interference phenomena from color antenna arrays and or Unruh noninertial color currents play a critical role in resolving the BES+DA+pA puzzle? We explore non-hydrodynamic scenarios that could generate apparent collective flow signatures in vn observables.

Speaker:
Prof.Miklos Gyulassy
(Columbia University)

Slides

16:30
→
18:30

Electromagnetic probes: 3helium

helium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Joachim Stroth
(Goethe-University and GSI)

slides

16:30

Measurements of direct-photon-hadron correlations and direct-photon azimuthal anisotropy by STAR20m

Many observations have indicated that the fragmentation functions in nucleus-nucleus collisions are softened compared to that in proton-proton collisions. Different theoretical models have been proposed in order to describe the observed phenomena. For a deeper insight into the underlying physics and better constraints for the extracted parameters of the medium formed in nucleus-nucleus collisions, a calibrated probe is needed. Direct photons act as such probes, providing experimental tools to explore energy loss of hard-scattered patrons.
We report systematic studies of azimuthal correlations of charged hadrons with respect to a direct-photon trigger in p+p and Au+Au collisions, using new data collected in 2008, 2009, and 2011. The nuclear modification factor of coincidence rate, $I_{AA}$, will be shown. We also report direct-photon azimuthal anisotropy as a function of transverse momentum at mid-rapidity with event plane reconstructed from particles at forward rapidity in Au+Au collisions using the STAR detector at RHIC. We discuss the results in the scope of current theoretical models.

Soft photon production from real-time dynamics of jet fragmentation20m

Soft photons produced in heavy ion collisions are an important tool in probing the properties of the quark-gluon plasma. For this purpose, it is crucial to understand the background - soft photons produced in elementary collisions. Low theorem states that soft photon production in hadron collisions is dominated by Bremsstrahlung off charged initial and final state hadrons. Surprisingly, almost every experiment observed an enhancement (by a factor of $2\div 5$) above Low theorem's prediction. This is the longstanding puzzle of "anomalous soft photon production." The phenomenon is not observed in processes with leptonic final states, which suggests that the mechanism is due to nonperturbative QCD evolution. We study this phenomenon using an exactly soluble, massless, Abelian model in $1+1$ dimensions which shares with QCD many important properties: confinement, chiral symmetry breaking, axial anomaly and $\theta$-vacuum. We then apply this model to the soft photon production in the fragmentation of jets produced in $Z^0$ decays and find a qualitative agreement with the data.

Speaker:
Frasher Loshaj
(Stony Brook University)

Slides

17:10

Z and W production in pp, pPb and PbPb collisions with CMS20m

The weak bosons, Z and W, do not participate in the strong interaction, and thus constitute
clean probes of the initial state of nuclear collisions. Detected trough their leptonic decay
channels, they provide constraints on the nuclear parton distribution functions (PDF). In
particular the W boson proves a unique constraint on the sea quark distributions.
We report on CMS measurements of weak boson production in pp, pPb and PbPb. Particular emphasis
is place on measurements of the 35 nb$^{-1}$ of pPb data collected at the beginning of 2013.
This provides access to a Bjorken x region, $10^{-3}$ -- 1, which is lacking precision
experimental measurements needed by nuclear PDF parametrizations.
The Z boson nuclear modification factors as a function of transverse momentum and rapidity will
be shown, together with forward to backward ratios. The W boson yields, charge asymmetries, and
forward to backward ratios in pPb collisions will also be reported. With a production cross
section an order of magnitude larger than the Z, the W allows precise comparisons to theoretical
predictions. Comparisons to PDFs are made for both Z and W measurements

Speaker:
Anna Zsigmond
(Wigner RCP, Budapest (HU))

Slides

17:30

Measurements of vector boson production in lead-lead and proton-lead collisions with the ATLAS detector20m

Photons and weak bosons do not interact strongly, and thus their production yields provide direct tests of binary collision scaling, and in addition should be sensitive to the nuclear modification of parton distribution functions (nPDFs). Proton-lead collisions also provide
an excellent opportunity to test nPDFs in a less dense environment than lead-lead, along with useful forward backward asymmetries in the final state.
The ATLAS detector has proven to be an excellent apparatus in measurements involving photons, electrons and muons, the latter being products of weak-boson decays, in the high occupancy environment produced in heavy ion collisions. The experiment has recorded 30 $nb^{-1}$ of proton-lead data and 140 $\mu b^{-1}$ of lead-lead data, both of which have similar integrated partonic luminosities. We will present the prompt photon, Z and W boson yields as a function of centrality, and also differentially in transverse momentum and rapidity, in lead-lead and proton-lead collisions from the ATLAS experiment. For W bosons also a lepton charge asymmetry has been studied, which may also shed light on nPDFs.

Speaker:
Iwona Grabowska-Bold
(AGH University of Science and Technology (PL))

Slides

17:50

The QCD phase diagram in the region of moderate temperature and high baryon density: study of dimuon production in the 20-160 AGeV interval at the CERN SPS20m

The structure of the QCD phase diagram in the region of moderate temperature and high baryon density is still almost unexplored. In this regime, the QGP and hadronic phases should be separated by a first order transition region. On the other hand, for sufficiently low baryonic chemical potential a simple cross-over is expected. The end point of the first order transition region is the so called critical point.
Measurements of the ratio $K^+/\pi^+$ vs energy performed at the CERN SPS by the NA49 collaboration showed that the early stage produced in central Pb-Pb collisions at $E_{lab}$=30-40 AGeV may have reached the transition line - marking the onset of deconfinement. However, this interpretation is still controversial. Dilepton measurements with a rich set of independent observables offer a completely independent way to shed light on the onset of deconfinement and at the same time on the issue of chiral restoration. The CERN SPS is unique for systematic investigations along these lines, due to its wide beam energy range from 20-160 AGeV coupled to very high luminosities over the full range.
The objective of this talk is to present a new proposal for measuring dimuon production in a comprehensive energy scan at the SPS - specifically both below and above the maximum of the $K^+/\pi^+$ ratio. To advance the field with measurements which could provide quantitative insight, a further significant increase in the precision and in the collected statistics with respect to the past reference experiment NA60 is needed. To this end, we propose a novel NA60-like apparatus, with improved performance, based on the coupling of a muon spectrometer to a a silicon pixel spectrometer in the vertex region before the absorber.
The first key element is a high-precision measurement of the temperature $T$ of the thermal dimuon continuum in the mass range $1.1\lt M\lt2.5$ GeV (IMR) vs. beam energy. The temperature is accessible through the spectral shape of the mass spectra, and since mass is a Lorentz-invariant, $T$ is immune to any motion of the emitting sources and thus purely thermal, in contrast to the slope parameters of dilepton $m_T$ spectra or photon $p_T$ spectra. At top SPS energies, values of about 200 MeV were found, indicating dominantly partonic emission sources. For decreasing beam energies one should expect that the partonic contribution will also decrease, becoming negligible at the onset of deconfinement. Thus the onset of deconfinement might be tagged by a precision measurement of $T$ in the IMR.
The second element is related to the transverse momentum spectra, which encode - besides temperature - also radial flow, another key property of the fireball. At topmost SPS energies the
effective temperature extracted from the $m_T$ spectra vs mass shows an increase up to $M\sim1$ GeV corresponding to $\rho$ production which is maximally coupled to radial flow through pions. At 1 GeV a sudden drop occurs and the temperature is constant at 180-200 MeV - a sign of production of thermal dimuons from the partonic medium without any flow (at the SPS). The evolution of the pattern of $T_{eff}$ vs. $M$ towards lower energies, in particular the possible decrease or disappearence of the drop, will be most revealing: thermal radiation from multi-pion processes should exhibit a monotonic increase of $T_{eff}$ vs $M$ so that around the onset of deconfinement the drop should vanish.
The new experiment should reach a sensitivity at the MeV level in the measurements of $T$ and $T_{eff}$ vs $M$. This will be possible integrating luminosities at least an order of magnitude larger than in case of NA60 or so while retaining a good signal to background ratio - well above than 1/100 in the IMR even in Pb-Pb central collisions.
For masses below 1 GeV (LMR), at high energies, hadronic many body models describe $\rho$ production and the notion that the total baryon density drives the broadening is now well accepted. At lower energies, the baryon density gets maximal, thus the effects of $\rho$ broadening can be measured with utmost precision.
In this measurement the mass resolution is a key factor and we propose to improve it over NA60 by a factor 2-3, reaching $\sim$10 MeV at the $\omega$ mass.
The experimental apparatus must have also a good $p_T$-$y$ coverage down to the lowest beam energies. In the talk the detector perfomance in terms of acceptances at different energies and mass resolution will be discussed in detail. The physics performance will be presented on the basis of simulations of Pb-Pb collisions at 20 and 40 AGeV including a background estimate and a modeling of the involved physics processes - in medium $\rho$ in the LMR, multi-pion processes and partonic radiation in the IMR. An overview of the possible detector technologies together with a cost estimate will be also presented. Finally, an experimental program consisting of measurements at different energies and/or different collision systems will be discussed in terms of beam time needed to collect the required event statistics.

Speaker:
Gianluca Usai
(Universita e INFN (IT))

Slides

18:10

Measurements of dileptons with the CBM-Experiment at FAIR20m

The Compressed Baryonic Matter (CBM) experiment at the upcoming Facility for Antiproton and Ion Research (FAIR) will explore the phase diagram of nuclear matter at very high net-baryon densities and moderate temperatures in nucleus-nucleus collisions at beam energies up to 45 A GeV . One of the key diagnostic probes of strongly-interacting matter at extreme conditions are dileptons. Dilepton measurements performed so far in heavy-ion collisions at various energies have found that the major challenge is to subtract the combinatorial background which overwhelms the interesting signals such as the rho spectral distribution, direct radiation from the fireball at intermediate invariant masses, and charmonia. This background is of different physical origin for dielectron and dimuons, and differs as function of invariant mass. Therefore, the systematic and statistical errors of the extracted signals will be substantially minimized by measuring both electron and muon pairs. The CBM detector is designed as a multi-purpose device which will be able to measure hadrons, electrons and muons in heavy-ion collisions. Electrons will be measured using a Ring Imaging Cherenkov (RICH) detector in combination with a Transition Radiation Detector. For muon measurements, the RICH detector will be replaced by a large area Muon detection system consisting of alternating layers of hadron absorbers and tracking chambers. The results of performance studies and the status of the detector developments will be presented.

platinum

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Federico Antinori
(Universita e INFN (IT))

announcement

16:30

Heavy-flavour correlations in pp, p-Pb and Pb-Pb collisions20m

Heavy quarks (charm and beauty) are excellent probes to study the properties of the strongly interacting matter formed in heavy ion collisions, which is expected to be a Quark-Gluon Plasma (QGP). Indeed, due to their large mass, charm and beauty quarks are produced in initial hard scattering processes among partons of the colliding nuclei, before the formation of the QGP, and they traverse the medium and interact with its constituents.
The ALICE Collaboration measured the production of open heavy-flavour hadrons via their hadronic and semi-leptonic decays at mid-rapidity in pp, p-Pb and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 7, 5.02 and 2.76 TeV respectively.
A strong suppression of the open charm hadron yields at high $p_{\rm T}$ was observed in Pb-Pb collisions relative to pp interactions: this effect is attributed to a substantial in-medium energy loss of the charm quarks.
Further insight into the effects of the medium on charm and beauty quarks can be obtained by measuring the angular correlations between open heavy-flavour hadrons and charged hadrons.
The comparison of the correlation function in pp and Pb-Pb collisions can provide deeper information on the way heavy quarks lose energy in the QGP and can spot possible modifications to the charm parton shower and hadronisation in the presence of the medium. Furthermore, by studying the correlations of electrons from heavy-flavour decays and the charged hadrons in pp, it is possible to statistically separate the charm and beauty contributions to the yield of heavy-flavour decay electrons, making this analysis an excellent tool to test pQCD calculations.
The observation of double-ridge long range correlations in p-Pb collisions for light-flavour hadrons could originate from a collective behaviour of the system, as well as from gluon saturation in the initial state (color glass condensate). The same effect can be studied for heavier quarks via the correlation between heavy-flavour hadrons (or their decay electrons) and charged particles.
Results from the correlation analyses, performed using the data collected with ALICE in pp collisions at $\sqrt{s}$ = 7 TeV, Pb-Pb at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, and in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be presented in this contribution.

Heavy flavor hadrons serve as valuable probes of the transport properties of the quark-gluon plasma (QGP) created in relativistic heavy-ion collisions. We introduce a comprehensive framework that describes their full-time evolution in the QGP matter and the subsequent hadronic phase. The heavy quark energy loss in a de-confined QCD medium is modeled with our improved Langevin approach [1] that simultaneously incorporates quasi-elastic scattering [2,3] and medium-induced gluon radiation [4]. The subsequent transport of heavy mesons in the hadron gas phase is described within the ultra-relativistic quantum molecular dynamics (UrQMD) model [5]. The intermediate hadronization process from heavy quarks to their respective mesonic bound states is calculated with our hybrid fragmentation plus coalescence model [1].
We investigate the relative contribution of each of these ingredients to the final-state spectra of heavy mesons and demonstrate that while quasi-elastic scattering dominates heavy quark energy loss in the QGP at low energies, contributions from gluon radiation at high energies are significant; the coalescence process is found important for heavy meson production at intermediate transverse momenta; and the subsequent hadronic interactions is equally crucial as the free quark evolution inside QGP for the development of heavy flavor suppression and collective flow behaviors that one observes. Within this newly developed framework, we provide a good description of D meson suppression and flow measured at both RHIC and LHC, as well as predictions for the future measurements of B mesons.
In addition, a new set of observables – heavy-flavor-tagged angular correlation functions – are explored and found to be potential candidates for distinguishing different energy loss mechanisms of heavy quarks inside a QGP medium [6]. We calculate correlation functions for D-D, D-e, D-hadron, e-hadron, etc., some of which can be compared to the existing preliminary data from LHC experiments.
1. S. Cao, G.-Y. Qin, and S. A. Bass, Phys. Rev. C88, 044907 (2013).
2. G. D. Moore and D. Teaney, Phys. Rev. C71, 064904 (2005).
3. S. Cao and S. A. Bass, Phys. Rev. C84, 064902 (2011).
4. B.-W. Zhang, E. Wang, and X.-N. Wang, Phys. Rev. Lett. 93, 072301 (2004).
5. S. A. Bass, et al., Prog. Part. Nucl. Phys. 41, 255-369 (1998).
6. S. Cao, G.-Y. Qin, S. A. Bass and B. Mueller, J. Phys. Conf. Ser. 446, 012035 (2013).

Speaker:
Shanshan Cao
(Duke University)

Slides

17:10

Correlations and higher-order flow: new heavy-quark observables in relation to the bulk dynamics20m

The progress made by experimental collaborations in measuring heavy-flavor particles in heavy-ion collisions with unprecedented precision is accompanied by the advancement of theoretical calculations. Our recently developed model, which couples a Monte-Carlo Boltzmann-propagation of heavy quarks to the 3+1d fluid dynamical evolution from fluctuating EPOS initial conditions reproduces well the experimental data for the traditional observables like the nuclear modification factor and the elliptic flow.
In this talk we will discuss correlations and higher-order flow harmonics as new heavy-quark observables and demonstrate their potential to reveal properties of the QGP. Our studies show that correlations of heavy-flavor particles are sensitive to the energy loss mechanism. Experimentally feasible correlation observables can thus discriminate between elastic and radiative processes and provide valuable information about the transport coefficients. Higher-order flow harmonics, $v_n$, quantify the degree of thermalization of heavy quarks beyond our current understanding of the built-up of elliptic flow. By selecting special classes of bulk events from the probability distribution of $v_n$ of light-flavor hadrons we discuss systematically how relating the light- and the heavy-flavor sector help us understand the interaction mechanisms and thermalization in the QGP.

Speaker:
DrMarlene Nahrgang

Slides

17:30

Gluon radiation by heavy quarks at intermediate energies20m

It is generally admitted that heavy quarks (c and b) created in the early stage of ultrarelativistic heavy ion collisions through hard processes are among the best probes of the later QGP stage. Perturbative QCD allows for the calculation of the production cross sections (in contradistinction to light quarks) and these cross sections have also been measured. Also the details of the chiral/confinement phase transition are less important than for light quarks because, due to its mass, the momentum of the heavy quark determines the momentum of the open charm hadrons. In addition, the momentum distribution at production and at the transition is very different from that expected if the heavy quarks are in thermal equilibrium with the plasma of light quarks and gluons. Therefore the modification of the initial momentum distribution by the interaction of the heavy quarks with the plasma carries information on the plasma properties.
The interaction of the heavy quark with the plasma has two parts, elastic collisions and radiative collisions. For the first a model was developed [1] in which the cross section of the elementary interactions are calculated by
perturbative QCD with a running coupling constant and an infrared behavior adjusted so as to match hard thermal loop calculations. Embedding these cross sections in the hydrodynamical description of the expanding plasma of Heinz and Kolb it was shown that the collisional energy loss underpredicts the measured energy loss of heavy mesons at large momenta as well as their elliptic flow by roughly a factor of two.
It is the purpose of the present work to extend our pQCD calculation toward the calculation of the radiative energy loss for heavy quarks at intermediate energies. To this end we compute the gluon emission cross section of a heavy quark colliding a light parton from the plasma in pQCD at leading order [2]. We first derive the high-energy approximation that naturally extends results obtained by Gunion and Bertsch for the light quark sector to heavy quarks. We next show that it is possible to compute the complete energy dependence of the result. This allows us to assess the range of applicability in energy of the high-energy approximation. We then extend the calculation to the case of intermediate energy, for which the invariant mass $s$ in the collision does not exceed the squared heavy quark mass $m_Q^2$ in large amounts. We discuss in particular the relevance of the dead cone effect as well as the consequences of a finite heavy quark energy, which is often neglected in the literature. For this purpose, we address quantities such as the average energy loss in a bath at finite temperature as well as the nuclear modification factor as a function of the transverse momentum.
References
==========
[1] P.B. Gossiaux and J. Aichelin, Phys Rev C78, 014904 (2008)
[2] J. Aichelin, P.B. Gossiaux and Th. Gousset arXiv:1307.5270, TBP in PRD

Speaker:
Pol Gossiaux
(Subatech)

Slides

17:50

Energy loss and (de)coherence effects beyond eikonal approximation20m

The parton branching process is known to be modified in the presence of a medium. Colour decoherence processes are known to determine the process of energy loss when the density of the medium is large enough to break the correlations between partons emitted from the same parent. In order to improve existing calculations that consider eikonal trajectories for both the emitter and the hardest emitted parton, we provide in this work, the calculation of all finite energy corrections for the gluon radiation off a quark in a QCD medium that exist in the small angle approximation and for static scattering centres. Using the path integral formalism, all particles are allowed to undergo Brownian motion in the transverse plane and the offspring allowed to carry an arbitrary fraction of the initial energy. The result is a general expression that contains both coherence and decoherence regimes that are controlled by the density of the medium and by the amount of broadening that each parton acquires independently.

I will discuss a holographic model of finite temperature and density QCD matter with a large and roughly equal number of colors and flavours. The basic framework of the model is 5-dimensional classical Einstein gravity with a black hole and with an AdS$_5$ boundary, on which the physical 4-dimensional quantum theory resides. The model further contains a scalar dilaton for asymptotic freedom and confinement, a scalar tachyon for chiral symmetry breaking and a charge density for chemical potential. Solving the classical gravity equations numerically leads to an identification of a chirally symmetric and chirally broken phase with a phase transition in between. The phase transition line on the $T,\mu$ plane can have both 2nd and 1st order segments. The computation can be extended down to the quantum phase transition at $T=0$. The dilaton and tachyon potentials are only constrained by physical properties, not uniquely determined. Until they are derived one cannot make definite predictions, the model rather is a framework for discussing various dynamical alternatives.

Speaker:
Prof.Keijo Kajantie
(Helsinki Institute of Physics)

Slides

16:30
→
18:30

Initial state physics: 2titanium

titanium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Kari J. Eskola
(University of Jyvaskyla)

slides

16:30

Production of light flavor hadrons at intermediate and high $p_{\rm T}$ measured with the ALICE detector20m

Light flavor transverse momentum spectra at intermediate and high $p_{\rm T}$
are important as baseline perturbative QCD measurements in pp, evaluating
initial state effects (nuclear p.d.f.'s) in p-Pb, and for investigating the
suppression in Pb-Pb collisions. In this talk results for all these
collisional systems will be presented.
The new measurement of $R_{\rm pPb}$ for unidentified charged particles
extended up to 50 GeV/$c$ will be presented together with the construction of
the reference pp spectrum at $\sqrt{s} = 5.02$ TeV. The final results on the
production of charged pions, kaons, and protons up to $p_{\rm T} = 20$ GeV/$c$
in pp and Pb-Pb collisions will also be reported and compared to recent QCD
and phenomenological calculations. The impact of these results on our
interpretation of jet quenching in Pb-Pb through $R_{\rm AA}$ and the
question of whether the proton-to-pion ratio can still be considered to be
anomalous will be discussed.

Centrality dependence of particle production in p-A collisions measured by ALICE20m

Measurements of particle production in proton-nucleus collisions
provide a reference to disentangle final state effects,
i.e. signatures of the formation of a deconfined hot medium, from
initial state effects, already present in cold nuclear matter. While
most of the benchmarks from the control experiment indicate that
initial state effects do not play a role in the observed suppression
of hadron production observed in heavy ion collisions, several
measurements of particle production in the low and intermediate $p_{\rm T}$
region indicate the presence of collective effects.
Since many initial state effects are expected to vary as a function of
the number of collisions suffered by the incoming projectile, it is
crucial to estimate event-by-event the centrality of the collision.
We present the centrality dependence of particle production in p-A
collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV measured by the ALICE experiment,
including the pseudo-rapidity and transverse momentum spectra, with a
special emphasis on the event classification in centrality classes and
its implications in the interpretation of the nuclear effects.

Speaker:
DrAlberica Toia
(Johann-Wolfgang-Goethe Univ. (DE))

Slides

17:10

Decoherence between the initial and final state radiation in a dense QCD medium20m

We study medium modifications to the interference pattern between initial and final state radiation. We compute single gluon production off a highly energetic parton that undergoes a hard scattering and subsequently crosses a dense QCD medium of finite size. Multiple soft scatterings with the medium are resumed within the harmonic oscillator approximation. We find the decoherence of correlated partons traversing the medium depends on two scales: the medium length $L$ and the decorrelation time of the gluon due to the medium $\tau_f$. This interplay gives origin to two different asymptotic limits of the gluon spectrum: the coherent ($\tau_f\gg L$) and incoherent regime ($\tau_f\ll L$). We discuss the main characteristics of each regime. We show that in both cases there is a gradual onset of decoherence between the initial and final state radiation due to multiple scatterings, that opens the phase space for large angle emissions. By examining the multiplicity of produced gluons, we observe a potentially large double logarithmic enhancement for dense media and small opening angles. This result points to a possible modification of the evolution equations due to a QCD medium of finite size. We comment on the phenomenological consequences (such as radiative energy loss) of this setup in pA collisions.

Speaker:
Mauricio Martinez Guerrero
(The Ohio State University)

Slides

17:30

Searching for the "Ridge" in d+Au collisions at RHIC by STAR20m

Long-range pseudo-rapidity ($\Delta\eta$) correlations at small azimuthal difference ($\Delta\phi$) are observed in high multiplicity p+p and p+Pb collisions at the LHC. Subtraction of the di-hadron correlation in low-multiplicity p+Pb collisions from high-multiplicity ones reveals a back-to-back double ridge structure ($\Delta\phi\approx 0$ and $\pi$). A similar double ridge is observed in high-multiplicity d+Au collisions by the PHENIX experiment in their limited acceptance. Differences between multiplicity-selected d+Au collisions (and p+p collisions) have been observed before by STAR. However, the question remains open whether the ridge in d+Au collisions is a jet-related difference between central and peripheral collisions, or a new physics phenomenon such as anisotropic flow in d+Au. STAR, with its large acceptance, can rigorously address this question.
In this talk, we report di-hadron $\Delta\eta$-$\Delta\phi$ correlations in d+Au collisions at $\sqrt{s_{NN}} =$ 200 GeV. At mid-rapidity (with $|\Delta\eta|<2$), the jet-like correlation contribution in ``central$-$peripheral" method is evaluated. At large $|\Delta\eta|\approx 3$, the comparison of di-hadron correlations in central and peripheral collisions is reported in terms of the Au and deuteron beam directions. The $\Delta\phi$ correlation functions are also analyzed via a Fourier series decomposition; the $|\Delta\eta|$ and multiplicity dependencies of the Fourier coefficients are investigated. These di-hadron correlations data over the large acceptance may elucidate the existence or lack of a ridge in d+Au collisions at RHIC.

Speaker:
Li Yi

Slides

17:50

A unified picture of parton multiple scattering in the small-x regime and forward physics at RHIC and the LHC20m

The quest for experimental signatures of small-x gluon saturation has been one of the major goals in p+A (d+A) programs at RHIC and LHC. Experimental measurements of single particle and two-particle correlations in the forward direction have revealed novel nuclear suppression patterns, which might help pinpoint the small-x gluon dynamics. At the moment there are two formalisms which can both describe reasonably well the nuclear suppression observed in these experiments. One is the so-called higher-twist factorization approach, which describes the parton multiple scattering in terms of the power corrections to the differential cross section [1,2]. The other one is the so-called small-x color glass condensate (CGC) approach [3]. So far the precise connection between these two approaches has not been established. In this talk, we demonstrate how the multiple parton scattering picture and the small-x gluon saturation picture are related and show how the transition from a dilute parton system to a dense gluon saturation region occurs. Our work unifies the two approaches in studying the nonlinear small-x parton dynamics. On the example of forward rapidity photon production in p+A collisions, we demonstrate that in the broad transition region between a dilute parton system and a deeply saturated regime the two approaches give identical results. This work also helps understand the constraints on the small-x phenomenological studies.
[1] J. Qiu and I. Vitev, Phys. Lett. B632, 507 (2006)
[2] Z. B. Kang, I. Vitev and H. Xing, Phys. Rev. D85, 054024 (2012)
[3] see, e.g., J. L. Albacete and C. Marquet, Phys. Rev. Lett. 105, 162301 (2010)

Speaker:
Zhongbo Kang
(L)

Slides

18:10

Dijets in p+Pb collisions and their quantitative constraints for nuclear PDFs20m

We present a perturbative QCD analysis concerning the production of high-pT
dijets in p+Pb collisions at the LHC. The next-to-leading order corrections, scale
variations and free-proton PDF uncertainties are found to have only a relatively
small influence on the normalized dijet rapidity distributions. Interestingly, however, these novel observables prove to retain substantial sensitivity to the nuclear effects in the PDFs. Especially, they serve as a more robust probe of the nuclear gluon densities at x > 0.01, than e.g. the inclusive hadron production. We confront our calculations with the recent data by the CMS collaboration. These preliminary data lend striking support to the gluon antishadowing similar to that in the EPS09 nuclear PDFs.

Anisotropic azimuthal correlations are used to probe the properties and the evolution of the system created in heavy-ion collisions.
Hydrodynamic model calculations predict that there are effects of $p_{\rm T}$ dependent fluctuations of the flow angle and flow magnitude, which might bias our previous anisotropic flow measurements.
In this talk, the two effects will be investigated in both Pb-Pb and p-Pb collisions, using two-particle azimuthal correlation measurements with the ALICE detector. In addition, the factorization of the two-particle Fourier harmonics $V_{n\Delta}$ for different values of $n$ into single-particle azimuthal anisotropies $v_{n}$, will be discussed. Our measurements, together with the comparison to hydrodynamic model calculations will open a new window on the study of the initial state fluctuations and the extraction of shear viscosity of the quark-gluon plasma at the LHC.

Speaker:
You Zhou
(NIKHEF and University of Utrecht (NL))

Slides

09:20

Factorization breakdown of two-particle correlations and flow phenomena in pPb and PbPb collisions with CMS20m

The technique of two-particle correlations has been widely used in studying flow via azimuthal anisotropy in relativistic heavy-ion collisions. A key assumption imposed in this approach is the factorization of Fourier coefficients extracted from two-particle correlations into a product of single-particle anisotropies of trigger and associated particles. It was recently predicted by hydrodynamics that due to initial-state participant fluctuations, a transverse momentum ($p_T$) dependence of the event-plane angle would be induced, leading to a breakdown of factorization, even if hydrodynamic flow is the only source of correlations. We present a systematic examination of the factorization assumption in 5.02 TeV pPb and 2.76 TeV PbPb collisions with the CMS experiment. Significant breakdown of factorization (up to 20%) is observed in a large sample of ultra-central (0--0.2%) triggered PbPb events, where initial-state fluctuations play a dominant role. Comparison of data and viscous hydrodynamics predictions, as a function of $p_T$ and centrality, allows new constraints on the modeling of initial condition and shear viscosity to entropy density ($\eta/s$) ratio of the medium created in heavy-ion collisions. Furthermore, the measurement is also extended to high-multiplicity pPb collisions. As the initial-state geometry of a pPb collision is expected to be entirely a consequence of fluctuations, quantitative studies of factorization breakdown will help to investigate the nature of the observed long-range correlations in pPb collisions, particularly in the context of hydrodynamic models.

Measurements of the distributions of event-by-event flow harmonics $v_n$
and the correlations between harmonics $v_n$ and $v_m$ of different
orders in $\sqrt{s_{NN}}=2.76$ TeV Pb+Pb collisions are presented. These
measurements give insight into the nature of fluctuations in the initial
geometry and the role of linear and non-linear hydrodynamic response to
the fluctuations, the latter can introduce correlations between flow
harmonics. The study of fluctuations is also extended by measurements of
the rapidity dependent fluctuations in the v_n. Furthermore, the
event-by-event fluctuations in the event shape is elucidated by
jet-tomography studies, where the correlations between the $v_n$ of
fully reconstructed jets and the $v_m$ of soft particles are measured.
The latter directly probes the path-length dependent jet quenching
response to the variation of the event-shape controlled by bulk particles.

Speaker:
Soumya Mohapatra
(State University of New York (US))

Slides

10:00

A perturbative approach to hydrodynamics20m

Initial fluctuations in hydrodynamic fields such as energy density or flow velocity give access to understanding initial state and equilibration physics as well as thermodynamic and transport properties. We provide evidence that the fluid dynamic propagation of fluctuations of realistic size can be based on a background-fluctuation splitting and a systematic perturbative expansion in the fluctuating fields. Initial conditions are characterized by a Bessel-Fourier expansion for single events, event-by-event correlations and probability distributions. The evolution equations can be solved order-by-order in the expansion which allows to study the fluid dynamical propagation of single modes, the study of interaction effects between modes, the determination of the associated particle spectra and the generalization of the whole program to event-by-event correlations and distributions. We also show comparisons to flow measurements at the LHC.

Speaker:
Stefan Floerchinger
(CERN)

Slides

10:20

Heavy ions collision evolution modeling with ECHO-QGP20m

We present a numerical code for modeling relativistic heavy ion
collisions, ECHO-QGP. The code includes relativistic hydrodynamics
with dissipative terms and implements Israel-Stewart theory
in 3+1 D. Initial conditions are provided through an implementation
of the Glauber model (both Optical and Monte Carlo), while freezeout
and particle generation is based on the Cooper-Frye prescription.
ECHO-QGP features dynamical metric tensor in a GR framework for
ideal hydro and it can work in Bjorken and cartesian frames for
the dissipative case. The code shows remarkable
stability and accuracy with the combination of a conservative
(shock-capturing) approach with the high-order methods. ECHO-QGP
is able to reproduce several known solutions of ideal and dissipative
hydrodynamics including the lately proposed Gubser test.
Ref.
L. Del Zanna, V. Chandra, G. Inghirami, V. Rolando, A. Beraudo, A. De
Pace, G. Pagliara, A. Drago and F. Becattini,
*"Relativistic viscous hydrodynamics for heavy-ion collisions with ECHO-QGP"*
Eur. Phys. J. C **73**, 2524 (2013)

Speaker:
MsValentina Rolando
(Università di Ferrara, INFN Ferrara)

Slides

09:00
→
10:40

Heavy flavor: 4platinum

platinum

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Sandra Padula
(UNESP - Universidade Estadual Paulista (BR))

announcement

09:00

Charmonia in pp, pPb and PbPb with CMS20m

The mechanisms through which charmonia production is modified in the high-density medium created
in ultra-relativistic heavy-ion collisions, are still not quantitatively understood. In order to
disentangle among different scenarios, a multi-dimensional analysis in a wide kinematic range is
needed, in pp, pA and AA collisions, looking at many observables that have different
sensitivities to the various aspects of charmonia production. We will report on the prompt
$J/\psi$ measurements with the CMS detector, using the 35 nb$^{-1}$ pPb data recorded in 2013
and the 150 $\mu$b$^{-1}$ of PbPb data recorded in 2011. The nuclear modification factors and
azimuthal anisotropy in PbPb collisions at 2.76 TeV will be presented. New measurements of the
forward to backward ratios in pPb collisions at 5.02 TeV will also be shown. The dependence of
all these observables on the prompt $J/\psi$ kinematics, as well as the event characteristics,
will be shown. In addition, the comparison of the excited charmonium state ($\psi(2S)$) and the
ground state ($J/\psi$) between PbPb and pp is updated, utilizing the pp sample from 2013, which
has a factor of 20 higher statistical precision than the 2011 pp data previously presented.

The ALICE Experiment at the Large Hadron Collider (LHC) provides unique capabilities to study
charmonium production at low transverse momentum. In the early and hottest phase of
nucleus-nucleus collisions the formation of a Quark-Gluon Plasma (QGP) is expected. Several QGP
induced effects, such as the melting of charmonium states due to color screening and/or a
(re)combination of uncorrelated charm and anti-charm quarks, can play a role. A suppression with
respect to pp collisions of charmonium states such as the J$/\psi$ was indeed observed in
heavy-ion collisions, with the corresponding measurements in pp and p-Pb collisions being crucial
for the understanding of the Pb--Pb results.
At central (forward) rapidity, corresponding to the range $|y| < 0.9$ ($ 2.5 < y < 4$) , J$/\psi$ are
reconstructed via their decay into two electrons (muons) down to zero transverse momentum
($p_\mathrm{T}$). We will present results on the inclusive J$/\psi$ nuclear modification factor
$R_\mathrm{AA}$ as a function of collision centrality, rapidity and transverse momentum
p_\mathrm{T}, as well as results on the J$/\psi$ $\langle p_\mathrm{T} \rangle$ in Pb-Pb
collisions at $\sqrt{s_\mathrm{NN}} = 2.76$ TeV. Furthermore, a separation of prompt and non-prompt
components is possible down to $p_\mathrm{T}$ = 1.3 GeV/$c$ at central rapidity and allows a
determination of the $R_\mathrm{AA}$ of beauty hadrons and prompt J$/\psi$. These measurements
provide, in combination with results from lower energies and theoretical predictions, detailed
information on the different mechanisms related to the presence of the hot medium produced in
heavy-ion collisions.

Speaker:
Julian Book
(Johann-Wolfgang-Goethe Univ. (DE))

Slides

09:40

Recent STAR measurements of $J/\psi$ production from Beam Energy Scan and U$+$U collisions20m

$J/\psi$ suppression in heavy-ion collisions due to color screening of quark and antiquark potential in the deconfined medium has been proposed as a signature of the QGP formation. Other mechanisms, such as the cold nuclear matter effect and charm quark recombination, are likely to contribute to the observed modification of $J/\psi$ production in heavy-ion collisions. Measurements of $J/\psi$ invariant yields in different collision energies, collision systems, and centralities can shed new light on the interplay of these mechanisms for $J/\psi$ production and medium properties.
In this presentation we report on new measurements of $J/\psi$ production at midrapidity ($|y| < 1.0$) from the Beam Energy Scan program (Au$+$Au collisions at $\sqrt{s_{NN}} =$ 39 GeV and 62.4 GeV) and U$+$U collisions at $\sqrt{s_{NN}}$ = 193 GeV at STAR. Centrality and transverse momentum dependence of $J/\psi$ invariant yields and the nuclear modification factor ($R_{AA}$) will be presented and compared to those for Au$+$Au collisions at $\sqrt{s_{NN}} =$ 200 GeV and to model calculations. The energy dependence of $J/\psi$ suppression will be discussed.

Speaker:
Wangmei Zha
(USTC/BNL)

Slides

10:00

Charmonium suppression in a hot medium: melting vs absorption20m

A colorless $c\bar c$ dipole propagating through a hot medium can be dissolved either due to Debye screening of the binding potential, or by inelastic (color exchange) interaction with the medium, which turns the dipole into a color-octet state (absorption). Both mechanisms
are included into the path-integral description of the in-medium propagation of the dipole, providing the real and imaginary parts of the light-cone potential respectively. We found that
absorption, which is frequently forgotten, leads to a considerably stronger suppression of $J/\Psi$
production in heavy ion collisions, than the effect of Debye screening.

Using the QCD sum rule with its operator product expansion reliably determined from lattice calculations for the pressure and energy density of hot QCD matter, we calculate the strength of the $J/\psi$ wave function at origin and find that it decreases with temperature when the temperature is above the transition temperature. This result is shown to follow exactly that obtained from the solution of the Schr\"odinger equation for a charm and anticharm quark pair with temperature independent quark mass using the free energy from lattice calculations as the potential and is in sharp contrast to that using the deeper potential associated with the internal energy, which shows an enhanced strength of the $J/\psi$ wave function at origin. Our result thus suggests that the free energy potential from lattice calculations is the appropriate heavy quark potential for analyzing the charmonium spectrum at finite temperature.

A compilation of predictions for charged hadron, identified light
hadron, quarkonium, photon,
jet and gauge boson production in $p+$Pb collisions at $\sqrt{s_{_{NN}}} = 5$
TeV was made available ahead of the LHC $p+$Pb run [1].
We will compare the predictions to the available
data and comment on the reliablity of the predictions.
[1] J. Albacete {\it et al.}, Int. J. Mod. Phys. E {\bf 22} (2013) 133007.

One of the signatures of the strongly interacting medium produced in central PbPb collisions is
the suppression of high-$p_{\rm T}$ jets and charged particles. In order to to disentangle the
initial state and final state effects in heavy ion collisions, the nuclear modification factor
of both jets and of charged-particles in pPb ($R_{\rm pPb}$) and PbPb ($R_{\rm PbPb}$)
collisions are presented. The spectra of both jets and charged-particles in pp collisions at
$\sqrt{s} = 2.76$, PbPb collisions at $\sqrt{s_{NN}} = 2.76$ TeV, and pPb collisions at
$\sqrt{s_{NN}} = 5.02$ TeV, have been measured with the CMS detector using high statistics
samples. The $R_{\rm pPb}$ of charged particles is determined by dividing the measured pPb
spectrum by a pp reference spectrum constructed using interpolation methods, or alternatively
from PYTHIA simulations.

Hard-scattered partons provide an ideal probe for the study of the Quark-Gluon Plasma because they are produced prior to the formation of the QCD medium in heavy-ion collisions. Early measurements conducted at RHIC experiments have provided compelling evidence of jet quenching. In more recent years LHC experiments have confirmed these observations at a higher collisional energy, which allows full jet reconstruction over a much wider kinematic range. Jets are reconstructed in ALICE utilizing both the central tracking system for the charged constituents and the Electromagnetic Calorimeter for the neutral constituents. One of the most important challenges of jet reconstruction in heavy-ion collisions is the large fluctuating background energy density coming from the underlying event. A data-driven method has been used to correct for it which, combined with the unfolding of the detector effects, makes it possible to compare with other experimental results and theoretical predictions. Jet spectra will be reported for Pb-Pb and for pp collisions at a center of mass energy of 2.76 ATeV. The pp measurement serves also as the baseline for the determination of the nuclear modification factor, which shows a strong suppression of jet production in central Pb-Pb collisions. Differential measurements relative to the event plane and centrality class, which make use of data triggered by the Electromagnetic Calorimeter, will aid further investigation of details of this suppression, e.g. regarding the path length dependence of parton energy loss.

Speaker:
Salvatore Aiola
(Yale University (US))

Slides

10:00

Measurement of inclusive jet suppression in Pb+Pb20m

Highly energetic jets produced in relativistic heavy ion collisions
provide an important tool to study the QCD medium created in these
collisions. These jets suffer energy loss and modification of their
parton shower through interactions with the medium— a phenomenon known
as jet quenching. A generic feature of such energy loss is the
reduction in jet production rates. In this talk, new ATLAS results
will be presented on the suppression of inclusive jet production rates
in Pb+Pb collisions at 2.76 TeV. Measurements of the nuclear
modification factor RAA for fully reconstructed jets will be
presented. These measurements cover a large kinematic range in jet
transverse momentum and are differential in jet rapidity and collision
centrality and provide sensitivity to the details of the quenching
mechanism including the values of medium transport coefficients.

Speaker:
Aaron Angerami
(Columbia University (US))

Slides

10:20

Hydrodynamics and jets in dialogue20m

We investigate both the medium-induced modifications of jets and the jet-induced modifications of the medium in heavy ion collisions at LHC energies with JEWEL.
JEWEL is a fully microscopic Monte Carlo event generator for jet evolution in a dense medium relying on perturbative concepts, that can take any model of the medium as input. We present a detailed comparison between a full viscous hydrodynamic calculation for central events and a simplified, computationally inexpensive model.
We also study the modification of the hydrodynamic expansion due to jet energy loss
by extracting the local energy and momentum transfer from the jet to the medium.
The latter can be used as a source term in the hydrodynamic equations and we discuss its influence.

Speaker:
Korinna Christine Zapp
(CERN)

Slides

09:00
→
10:40

QCD phase diagram: 1helium

helium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Tetsuo Hatsuda
(Unknown)

announcement

09:00

Probing dense matter in compact star cores with radio pulsar data20m

Astrophysical observations of compact stars provide, in addition to collider experiments, the other big source of information on matter under extreme conditions. The largest and most precise data set about neutron stars is the timing data of radio pulsars. We show how this unique data can be used to learn about the ultra-dense matter in the compact star interior. The method relies on astro-seismology based on special global oscillation modes (r-modes) that emit gravitational waves. They would prevent pulsars from spinning with their observed high frequencies, unless the damping of these modes, determined by the microscopic properties of matter, can prevent this. We show that for each form of matter there is a distinct region in a frequency/spindown-rate diagram where r-modes can be present. We find that stars containing quark matter are consistent with both the observed radio and x-ray data, whereas for standard neutron stars so far unestablished, enhanced damping mechanisms would be required.

Speaker:
Kai Schwenzer
(W)

Slides

09:20

$\Lambda$($K_{S}^{0}$)-$h^{\pm}$ azimuthal correlations with respect to event plane and searches for chiral magnetic and vortical effects20m

QCD allows for the formation of parity-odd domains inside the Quark-Gluon Plasma (QGP). The proposed Chiral Magnetic Effect (CME) will lead to charge separation with respect to the reaction plane. Previous measurements from RHIC and LHC using charge-dependent two-particle azimuthal correlations with respect to the reaction plane are consistent with the expectation of charge separation from CME. However, the magnitude of the background correlation has not been understood and there is no reliable experimental approach to separate the background from a CME signal.
$\Lambda$($K_{S}^{0}$)-$h^{\pm}$ azimuthal correlations are expected to provide another estimate on the intrinsic background from particle correlations. In addition, theoretical calculations of the Chiral Vortical Effect (CVE) predict a difference in baryon versus anti-baryon azimuthal correlations with respect to the reaction plane. We will present the first measurements of $\Lambda$($K_{S}^{0}$)-$h^{\pm}$ and $\Lambda$-proton azimuthal correlations with respect to the event plane from Au+Au collisions at 39~GeV and 200~GeV from STAR to investigate the CME and CVE predictions. The physics implications of our measurements will also be discussed.

Speaker:
Feng Zhao
(University of California, Los Angeles)

Slides

09:40

Effects of magnetic fields on the quark-gluon plasma20m

In this talk recent lattice QCD results are presented about the response of the thermal QCD vacuum to external (electro)magnetic fields. Characteristic features of this response include the reduction of the deconfinement transition temperature due to the magnetic field and the paramagnetic nature of the QCD vacuum as a medium. The latter results in a squeezing of the quark-gluon plasma if the field is not uniform. Possible implications of this squeezing for heavy-ion collisions are discussed.

Theoretical studies [1] indicate that in relativistic heavy collisions a chiral magnetic wave at finite baryon density could induce an electric quadrupole moment, which will lead to a difference in elliptic flow of hadrons with opposite charge. The magnitude of this difference is predicted to be proportional to the charge asymmetry $A_\mathrm{ch}$, defined as $A_\mathrm{ch} \equiv \langle \left (N_{+} -N_{-} \right )/\left ( N_{+} +N_{-} \right ) \rangle$. Charge-asymmetry dependency of the pion elliptic flow has been observed in Au+Au collisions at the STAR experiment. On the other hand, it is argued that the local charge conservation at freeze-out, together with the characteristic shape of $v_{2}(\eta)$ and $v_{2}(p_\mathrm{T})$, may also contribute to elliptic flow splitting as a function of $A_\mathrm{ch}$. This can be manifested by implementing the corresponding measurement for higher flow harmonics $v_{3}$ [2].
Here, we present STAR's measurements of $v_{2}$ and $v_{3}$ for charged pions and kaons at low transverse momentum range (0.15 $< p_\mathrm{T} <$ 0.5 GeV/c), as a function of event charge asymmetry ($A_\mathrm{ch}$) in both U+U collisions at $\sqrt{s_\mathrm{NN}}$ = 193 GeV and Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 200 GeV. Our measurements for both collision systems serve as important consistency checks for the phenomena suggested as the consequence of the chiral magnetic wave.
[1] Burnier Y, Kharzeev D E, Liao J and Yee H U 2011 $\it{Phys. Rev. Lett}$ $\bf{ 107}$ 052303
[2] Bzdak A and Bozek P 2013 $\it{Physics Letters B}$ $\bf{ 726}$ 239-243

Speaker:
Qi-Ye Shou
(SINAP, BNL)

Slides

10:20

Quarks in strong magnetic fields20m

It has been known that magnetic fields enhance the chiral symmetry breaking (ChSB). According to studies of QED or models of the 4-fermi interactions, it was expected that the enhanced ChSB would resist the chiral restoration effects, increasing critical temperatures for the chiral restoration and deconfinement. Recent lattice calculations, however, showed the opposite behavior: the critical temperatures are reduced as a magnetic field increases. I will discuss how to resolve this apparent paradox, emphasizing which characteristic features of QCD make differences from other models.

Speaker:
Toru Kojo
(Bielefeld University)

Slides

10:40
→
11:10

Coffee break
30m

11:10
→
13:10

Correlations and fluctuations: 1europium

europium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Ulrich Heinz
(The Ohio State University)

announcement

11:10

Charge-dependent anisotropic flow and the search for the Chiral Magnetic Wave in ALICE20m

While no P- or CP-violation has ever been observed in the strong
sector of the Standard Model, there is no first principles reason
for it not to be present. Theoretical calculations have shown the
possibility of P-violating bubbles in the QCD vacuum, which in
combination with the strong magnetic field created in off-central
heavy-ion collisions leads to the Chiral Magnetic Effect (CME).
In addition, a coupling between the CME and the related
Chiral Separation Effect produces a wave-like excitation called
the Chiral Magnetic Wave (CMW). The CMW produces a quadrupole
moment that always has the same sign and is therefore present in
an average over events. In this talk we present a series of
charge-dependent anisotropic flow measurements in Pb-Pb
collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV in ALICE. The relation of these
measurements to the search for the CMW is discussed.

The hot QCD matter produced in any heavy ion collision with a nonzero impact
parameter is produced within a strong magnetic field.
We study the imprint that these fields leave on the azimuthal distributions and
correlations of the produced charged hadrons.
The magnetic field is time-dependent and the medium is expanding, which leads to the induction of
charged currents due to the combination of Faraday and Hall effects. We find that these currents
result in a charge-dependent
directed flow $v_1$ that is odd in rapidity and odd under charge exchange.
It can be detected by measuring
correlations between the directed flow of charged hadrons at different rapidities,
$\langle v_1^\pm (y_1) v_1^\pm (y_2) \rangle$

Speaker:
Umut Gursoy
(University of Utrecht (NL))

Slides

11:50

Measuring and interpreting charge dependent anisotropic flow as a function of the event charge asymmetry20m

Recently, the STAR Collaboration has reported a strong dependence of
the elliptic flow of positive and negative pions on the net charge
density [1]. This measurement attracted a lot of community attention,
as the signal appeared to be of the magnitude and the sign of that
predicted by the theory of the Chiral Magnetic Wave [2]. At the same
time the interpretation of the results and further detailed study of
the effect is rather difficult as the observable itself, the slope of
elliptic flow value on the observed charge asymmetry in the STAR TPC
acceptance, depends on the tracking efficiency and detector
acceptance. In this talk we show how one can first make the observable
robust (efficiency independent) and then make it suitable for many
differential studies, not possible before. We use this observable, a
three-particle correlator, in our model calculations to show the
sensitivity of the signal to several background effects, such as local
charge conservation, and propose experimental tests for further
identification of the effects responsible for the observed signal.
[1] G.~Wang [STAR Collaboration], ``Search for Chiral Magnetic Effects
in High-Energy Nuclear Collisions,'' Nucl.\ Phys.\ A904-905 {\bf
2013}, 248c (2013).
[2] Y.~Burnier, D.~E.~Kharzeev, J.~Liao and H.~-U.~Yee, ``Chiral
magnetic wave at finite baryon density and the electric quadrupole
moment of quark-gluon plasma in heavy ion collisions,''
Phys.\ Rev.\ Lett.\ {\bf 107}, 052303 (2011).

Speaker:
Prof.Sergei Voloshin
(Wayne State University)

Slides

12:10

Azimuthal anisotropy of charged particles from multiparticle correlations in pPb and PbPb collisions with CMS20m

Motivated by two- and four-particle azimuthal correlation measurements that suggest possible collective flow for charged particles emitted in pPb collisions at $\sqrt{s_{NN}}$ =5.02 TeV, we extend the correlation results for these collisions using the six- and eight-particle cumulant methods, and the Lee-Yang Zeros method. CMS has an extensive program studying azimuthal harmonic coefficients for both PbPb and pPb collisions using various methods. The current pPb results will be presented in this context. The data were collected by the CMS experiment at the LHC using both minimum bias and high-multiplicity collision triggers over a wide range in pseudorapidity. The results are compared to 2.76 TeV semi-peripheral PbPb collision data collected in 2011 covering a similar range of particle multiplicities. The second-order azimuthal anisotropy Fourier harmonic ($v_{2}$) is shown for the different methods. A comparison of the six- and greater particle correlations to the previously published two- and four-particle correlation results sheds light on the multiparticle nature of the azimuthal anisotropy. The results are also discussed in terms of recent calculations that explore the role of participant fluctuations on measurements of higher-order particle correlations in pPb collisions.

Speaker:
Quan Wang
(University of Kansas (US))

Slides

12:30

Flow harmonics in Pb+Pb collisions at energy of sqrt(sNN) = 2,76 TeV with the ATLAS detector20m

We report on measurements of the anisotropy of charged particles in lead-lead collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, using multi-particle cumulants calculated with the generating function method. The results on the transverse momentum, pseudorapidity and centrality dependence of the elliptic flow (v2) obtained from two-, four-, six- and eight-particle cumulants are presented. Higher-order coefficients, v3 and v4 are also derived using two- and four-particle cumulants and shown as a function of centrality and transverse momentum. A reduction of contributions not related to the initial geometry for vn studied with cumulant expansion of correlations between more than two particles is discussed. Event-by-event fluctuations of the flow harmonics evaluated with multi-particle cumulants as a function of transverse momentum and the collision centrality are also presented. These results are complemented with the pT-integrated elliptic flow measured in the pseudorapidity range |$\eta$|< 2.5 with the event plane method, exploring the range of very low transverse momenta. This was achieved by applying dedicated track reconstruction methods. The centrality dependence of the integrated v2, spanning the range of 0–80% of most central Pb+Pb collisions, is compared to other measurements obtained with higher $p_T$ thresholds. The pseudorapidity dependence of the integrated elliptic flow in different centrality intervals is discussed and compared to the lower energy RHIC data.

Speaker:
Dominik Karol Derendarz
(Polish Academy of Sciences (PL))

Slides

12:50

New universal parametrization of initial-state fluctuations and its application to event-by-event anisotropy20m

We propose a new, universal parametrization of the probability distribution of initial anisotropies in proton-proton, proton-nucleus and nucleus-nucleus collisions. The distribution of fluctuation-driven anisotropies, such as the initial triangularity $\varepsilon_3$, is described by a one-parameter power distribution. When a mean anisotropy in the reaction plane is also present, as in the case of the the initial eccentricity $\varepsilon_2$ in nucleus-nucleus collision, a new parameter must be added: the power distribution is replaced by a new, elliptic power distribution. Our results are in excellent agreement with all Monte-Carlo models of the initial state (Glauber, KLN, IP-Glasma) for all collision systems and all centralities.
We then apply our results to the interpretation of the event-by-event distributions of $v_2$ and $v_3$ recently measured by the ATLAS collaboration in Pb-Pb collisions at the LHC. Assuming that anisotropic flow is proportional to the initial anisotropy, $v_n=C_n\varepsilon_n$,
we obtain excellent fits to these data. This procedure gives us direct information on the initial state from data. Our results are compared to several initial-state models. We are also able to extract the hydrodynamic response $C_n$ for $n=2,3$ as a function of centrality, without assuming any particular model for the initial state. These results are compared with viscous hydrodynamic calculations of the response.
L. Yan and J. Y. Ollitrault,
"Universal fluctuation-driven eccentricities in proton-nucleus and nucleus-nucleus collisions,''
arXiv:1312.6555 [nucl-th], to appear in Phys. Rev. Lett.
L. Yan, A. M. Poskanzer and J. Y. Ollitrault, in preparation.

Speaker:
Li Yan

Slides

11:10
→
13:10

Jets: 2titanium

titanium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
John William Harris
(Yale University (US))

announcement

11:10

Jet quenching from the lattice20m

We present a lattice study of the momentum broadening experienced by a hard parton in the quark-gluon plasma. In particular, the contributions to this real-time phenomenon from soft modes are extracted from a set of gauge-invariant operators in a dimensionally reduced effective theory (electrostatic QCD), which can be simulated on a Euclidean lattice. At the temperatures accessible to present experiments, the soft contributions to the jet quenching parameter are found to be quite large. We compare our results to phenomenological models and to holographic computations.

Speaker:
Marco Panero
(IFT UAM/CSIC)

Slides

11:30

Measurements of charged particle spectra and nuclear modification factors in proton-lead and lead-lead collisions with the ATLAS detector20m

The measurement of charged particle spectra in heavy ion collisions carries important information about the properties of hot and dense matter created in these interactions. Spectra measured in lead-lead collisions at different centralities can be compared to the proton-proton spectra giving quantitative information about the properties of such matter. Proton-nucleus collisions provide further means for understanding the role of the initial state effects modifying the hard scattering rates.
The ATLAS detector at the LHC obtained the sample of Pb+Pb data at
$\sqrt{s_{\rm NN}}$ = 2.76 TeV with integrated luminosity 0.15 $nb^{-1}$, which can be compared to recently obtained pp sample of 4.5 $pb^{-1}$ sample at the same energy. The p+Pb data at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with integrated luminosity 30 $nb^{-1}$ can also be compared to the pp data obtained by interpolating pp measurements at $\sqrt{s}$ = 2.76 TeV and 7 TeV. Due to the excellent capabilities of the ATLAS detector, and its stable operation in heavy ion as well as proton-proton physics runs, the data allow measurements of the nuclear modification factor out to transverse momentum limited only by the statistics of the accumulated samples and studying the ratios of HI charged particle spectra divided by pp reference in different centrality bins over a wide range of pseudorapidity.

Speaker:
Petr Balek
(Charles University (CZ))

Slides

11:50

Qualitative extraction of qhat from combined jet quenching at RHIC and LHC20m

On behalf the JET Collaboration
Within five different approaches to parton propagation and energy loss in dense matter, a phenomenological study of experimental data on suppression of large $p_T$ single inclusive hadrons in heavy-ion collisions at both RHIC and LHC was carried out. The evolution of bulk medium used in the study for parton propagation was given by 2+1D or 3+1D hydrodynamic models which are also constrained by experimental data on bulk hadron spectra. Values for the jet transport parameter $\hat q$ at the center of the most central heavy-ion collisions are extracted or calculated within each model, with parameters for the medium properties that are constrained by experimental data on the hadron suppression factor $R_{AA}$. For a quark with initial energy of 10 GeV we find that $\hat q\approx 1.2 \pm 0.3$ GeV$^2$/fm at an initial time $\tau_0=0.6$ fm/$c$ in Au+Au collisions at $\sqrt{s}=200$ GeV/n and $\hat q\approx 1.9 \pm 0.7 $ GeV$^2$/fm in Pb+Pb collisions at $\sqrt{s}=2.76 $ TeV/n. Compared to earlier studies, these represent significant convergence on values of the extracted jet transport parameter, reflecting recent advances in theory and the availability of new experiment data from the LHC.

Recent data on the azimuthal and transverse momentum dependence of high-pT pion nuclear modification factors and high-pT elliptic flow in nuclear collisions at RHIC and LHC are analyzed in terms of a generic dE/dx model that interpolates between running coupling pQCD-based models such as CUJET2.0 and AdS/CFT-inspired holographic models. The jet-energy loss models are coupled to state of the art viscous hydrodynamic fields. RHIC data are found to be surprisingly consistent with most dE/dx+Hydro models, but extrapolations to LHC energies favor running coupling QCD-based energy-loss models, while conformal holography models are inconsistent with the data. It is also shown that energy-loss fluctuations appear to play a crucial role in the underprediction of high-pT elliptic flow as seen by various pQCD-based energy-loss approximations.

Speaker:
Barbara Betz
(Frankfurt University)

Slides

12:30

Centrality and rapidity dependence of inclusive jet production in p+Pb collisions at 5.02 TeV with the ATLAS detector20m

Measurements of reconstructed jets in high-energy proton-nucleus
collisions over a wide rapidity and transverse momentum range are a
fundamental probe of the partonic structure of nuclei. Inclusive jet
production is sensitive to the modification of parton distribution
functions in the high-density nuclear environment. In the forward
direction and at small pT jets may even explore the transition from a
dilute to saturated partonic system. Furthermore, any modification of
jet production in p+A collisions has implications for our
understanding of the strong suppression seen in central A+A
collisions. We present the latest results on inclusive jet production
in 31/nb of proton-lead collisions at 5.02 TeV with the ATLAS detector
at the LHC. The centrality of p+Pb events is determined by applying
the Glauber model to the sum of the transverse energy in the Pb-going
forward calorimeter. The jet yields in central and peripheral p+Pb
collisions are found to be suppressed and enhanced, respectively,
relative to geometric expectations. Furthermore, the modifications at
all rapidities are seen to be consistent with a simple function of the
total jet energy.

Centrality, rapidity and pT dependence of isolated prompt photon production in lead-lead collisions at sqrt(sNN)= 2.76 TeV with the ATLAS detector at the LHC20m

ATLAS has measured prompt photon production in sqrt(s_NN) = 2.76 TeV Pb+Pb collisions using data collected in
2011 with an integrated luminosity of 0.14 nb-1. The measurement is performed with a hermetic, longitudinally
segmented calorimeter, which gives excellent spatial and energy resolution, and detailed information about the
shower shape of each measured photon. A multi-parameter selection on a set of nine shower properties,
coupled with an isolation criterion based on the energy deposited in the cone around a photon, gives measured
purities ranging from 50% at low pT to greater than 90% at high pT. Photon yields, scaled by the mean nuclear
thickness function, will be presented as a function of collision centrality, pseudorapidity (in two intervals |eta| < 1.37
and 1.52 < |eta|< 2.37) and transverse momentum (from 22 < pT < 280 GeV). The scaled yields will be compared to
expectations from JETPHOX (perturbative QCD calculations at next to leading order), as are the ratios of the
forward yields to those near mid-rapidity.

In this talk, we first argue that a domain structure, which can be inferred from the properties of the Polyakov loop and and is called center domains, is created in the deconfined QCD matter in the early stage of ultrarelativistic heavy ion collisions. Its formation is assisted by the gauge configuration in the glasma state created right after the collisions. Then we show that the center domains are an important facet of the evolution of the quark-gluon plasma from its birth up to hadronization. They naturally explain the strongly coupled nature of the quark gluon plasma including its major observed properties from its nearly ideal hydrodynamical behavior to strong jet quenching.

Speaker:
Masayuki Asakawa
(Osaka University)

Slides

11:30

New approach to lattice QCD thermodynamics from Yang-Mills gradient flow20m

A novel method to study the bulk thermodynamics in lattice gauge theory is proposed on the basis of the Yang-Mills gradient flow with a fictitious time t. The energy density (epsilon) and the pressure (P) of SU(3) gauge theory at fixed temperature are calculated directly on 32$^3 \times$ (6,8,10) lattices from the thermal average of the well-defined energy-momentum tensor ($T_{\mu \nu}^R(x)$) obtained by the gradient flow. It is demonstrated that the continuum limit can be taken in a controlled manner from the t-dependence of the flowed data.
[1] M. Asakawa, T. Hatsuda, E. Itou, M. Kitazawa and H. Suzuki [FlowQCD Coll.], arXiv:1312.7492 [hep-lat].

Speaker:
DrTetsuo Hatsuda
(RIKEN)

Slides

11:50

Collisions in AdS: the road to experiments20m

Holography has been used for a while as a strongly coupled approach to study the initial stage of heavy-ion collisions. As holographic calculations cannot directly describe QCD, importantly neglecting any weak-coupling effects, it is an interesting question how well these studies fit experimental data. Here, we will focus on longitudinal dynamics, modeled by colliding shock waves in AdS.
These collisions give a surprisingly universal rapidity profile, where the shape at high collision energies is completely independent of the energy or longitudinal structure of the colliding shocks. It is somewhat complicated to compare this initial profile to the final measured rapidity profile, but we can compute the entropy and thereby make an estimate of the total multiplicity. The result indicates that our infinite coupling profile has somewhat more stopping than in real heavy-ion collisions, which is most likely because of neglecting weak-coupling effects. We finally comment on (future) consequences for real nucleus-nucleus and proton-nucleus collisions.
References: arxiv:1312.2956 and 1305.4919 (PRL 111)

Speaker:
Wilke van der Schee
(Utrecht University)

Slides

12:10

Rapidity evolution of Wilson lines at the next-to-leading order: Balitsky-JIMWLK equation at NLO20m

Scattering amplitudes of proton-Nucleus or Nucleus-Nucleus collisions at high-energy are described by matrix elements of Wilson line operators - infinite gauge factors ordered along the straight lines of the fast moving particles. The energy dependence of such amplitudes is described by the evolution equation of Wilson lines with respect to the rapidity parameter - the Balitsky-JIMWLK evolution equation. Most of the current phenomenology of high-energy and high-density QCD is based on the leading-order evolution equation with only running coupling corrections. In my talk I will present the derivation of the Balitsky-JIMWLK evolution equation at the next-to-leading order.

Speaker:
Giovanni Antonio Chirilli
(The Ohio State University)

Slides

12:30

Relating classical strings and gravitons in AdS/CFT jet quenching20m

Here's a fun question in gravity: What happens when a high-momentum graviton falls into a large (AdS-)black hole? Answer: Tidal forces outside the black hole can stretch the graviton from a quantum string into a large, classical string. What does this have to do with theory investigations related to jet quenching in strongly coupled plasmas? It provides a link between two very different methods that have been used to set up "jet stopping" problems in such plasmas---methods which have given parametrically different results.

Speaker:
Peter Arnold
(University of Virginia)

Slides

12:50

Thermalization of over-occupied gluons20m

In the weak coupling limit, the color-glass condensate framework predicts that the initial conditions of heavy-ion collisions are characterized by intense gauge fields, or equivalently high occupation numbers of gluons.
In my talk, I will describe how such initial conditions relax towards thermal equilibrium. In particular, I will discuss how such a system has dual descriptions in terms of either classical gauge field theory or effective kinetic theory of gluons. The domain of validity of the two descriptions is overlapping and I will numerically demonstrate the equivalence in the case of a non-expanding system.

Speaker:
Eero Aleksi Kurkela
(CERN)

Slides

11:10
→
13:10

QCD at high temperature and/or densityhelium

helium

darmstadtium

We present results of a three-loop hard-thermal-loop perturbation theory (HTLpt) calculation of the thermodynamic potential of a finite temperature and chemical potential system of quarks and gluons. We compare the resulting pressure, energy density, etc., and the diagonal/off-diagonal quark susceptibilities with lattice data. We show that there there is good agreement between the three-loop HTLpt analytic result and available lattice data.

Speaker:
Michael Strickland
(Kent State University)

Slides

11:30

Hadronic resonance production measured by ALICE at the LHC20m

Hadronic resonances constitute a valuable probe for the properties of the medium formed in heavy-ion collisions. In particular, they provide information on particle-formation mechanisms, the properties of the medium at freeze-out, and they contribute to the systematic study of energy loss and recombination. The study of resonance production in other collision systems such as pp and p-Pb form a necessary baseline to disentangle initial-state effects from genuine medium-induced effects.
The ALICE experiment has measured the production of the K(892)$^{0}$ and $\phi$(1020) resonances at mid-rapidity in different collision systems at LHC energies. Resonances are reconstructed via their hadronic decay in a wide momentum range, by exploiting the excellent particle-identification capabilities of the Time-Projection Chamber and the Time-of-Flight system. The first results on K(892)$^{0}$ and $\phi$(1020) production in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV at the LHC will be presented. The resonance mass and width, transverse momentum spectra and yields are measured and reported as a function of the multiplicity of the p-Pb collision. Ratios of resonance to long-lived hadron production in Pb-Pb are compared with the same quantities measured in pp and p-Pb collisions, in order to investigate re-scattering effects. The nuclear modification factors ($R_{\rm AA}$, $R_{\rm pPb}$), recently measured up to high $p_{\mathrm{T}}$ for resonances, are compared to the same measurement for long lived hadrons. The results are discussed in comparison with measurements at lower energies and theoretical predictions.

Speaker:
Francesca Bellini
(Universita e INFN (IT))

Slides

11:50

The QCD Equation of State at $\mathbf{\mathcal{O}(\mu_B^4)}$20m

Hydrodynamic models of heavy-ion collisions have increasingly begun to rely on lattice results for the Equation of State[1]. While the lattice has the advantage of being a first-principles approach to QCD, the notorious sign problem prevents a direct determination of the equation of state and other thermodynamic observables at finite baryon chemical potential $\mu_B$.
In our talk, we will present results from a high-statistics calculation of all the Taylor coefficients upto sixth order in a $(\mu_B,\mu_Q,\mu_S)$-expansion of the pressure. Our calculation allows us to extrapolate, for the first time, the equation of state on the freezeout curve upto $\mathcal{O}(\mu_B^4)$ while our sixth-order results show that the truncation error is not more than a few % upto $\mu_B/T\sim1.5$. Thus our equation of state should be useful in describing both the LHC results as well as results from RHIC beam energy scan down to $\sim$20 GeV. We will also use our results to construct the isentropic equation of state for strangeness-neutral systems.
Our lattice QCD calculations make use of the gauge ensembles generated using the HISQ action[2,3]. Our lattice sizes range from $6\times24^3$ to $12\times48^3$. The pion mass ($\sim$160 MeV) is nearly equal to its physical value while the strange quark mass has been set to exactly its physical value.
**References**
[1] See for e.g. C. Gale, S. Jeon and B. Schenke, Int. J. Mod. Phys. **A28**, 1340011 (2013); C. Shen, U. Heinz, P. Huovinen and H. Song, Phys. Rev. **C82**, 054904 (2010).
[2] A. Bazavov *et al.* [HotQCD Collaboration], Phys. Rev. **D86**, 035409 (2012).
[3] A. Bazavov, H.-T. Ding, P. Hegde, O. Kaczmarek, F. Karsch, E. Laermann, Y. Maezawa, S. Mukherjee, H. Ohno, P. Petreczky, C. Schmidt, S. Sharma, W. Soeldner and M. Wagner, Phys. Rev. Lett. **111**, 082301 (2013).

Speaker:
DrPrasad Hegde
(Central China Normal University)

Slides

12:10

Simulating full QCD at nonzero density using the complex Langevin equation20m

The complex Langevin method is extended to full QCD at non-zero
chemical potential. The method evades the sign problem which
makes naive simulations at nonzero density impossible.
The procedure 'gauge cooling' is used to stabilize the simulations
at small enough lattice spacings.
The method allows simulations also at high densities, all the way up
to saturation. The method is validated in the small chemical potential
region, where the sign problem is mild, and the reweighting approach is also feasible.

Speaker:
Denes Sexty
(University of Heidelberg)

Slides

12:30

Vector screening masses in the quark-gluon plasma and their physical significance20m

Static and non-static thermal screening states that couple to the
conserved vector current are investigated in the high-temperature
phase of QCD. Their masses and couplings to the current are determined
at weak coupling, as well as using two-flavor lattice QCD simulations.
A consistent picture emerges from the comparison, providing evidence
that non-static Matsubara modes can indeed be treated perturbatively.
We elaborate on the physical significance of the screening masses.

Speaker:
Prof.Harvey B. Meyer
(Joh. Gutenberg University Mainz)

Slides

12:50

The QCD equation of state20m

The quark-gluon plasma (QGP), the deconfined high-temperature phase of QCD, is currently under extensive investigation in heavy-ion collision experiments at RHIC and LHC. The transition from the hadronic, low-temperature phase to the QGP is a rapid crossover, manifested by a significant change in bulk thermodynamic quantities. A fundamental characteristic of QCD is the equation of state, which is also an essential ingredient of hydrodynamic modeling of heavy-ion collisions.
We report our final result for the 2+1 flavor QCD equation of state in the continuum limit. We calculate the pressure, energy density and other thermodynamic quantities in the experimentally relevant temperature range $140-400$ MeV. We use the highly improved staggered quark (HISQ) action with the Goldstone pion mass tuned to about $160$ MeV in the continuum limit. To perform the continuum extrapolation we use lattices with temporal extent $N_\tau=6$, $8$, $10$ and $12$.

Speaker:
Alexei Bazavov
(University of Iowa)

Slides

13:10
→
14:20

Lunch
1h 10m

14:20
→
16:00

Correlations and fluctuations: 2europium

europium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
George Fai
(U)

announcement

14:20

Pseudorapidity dependence of near-side and away-side long-range correlations in pPb collisions with CMS20m

Two-particle long-range pseudorapidity ($\Delta$$\eta$) correlations are observed in pPb collisions at the LHC. Previous correlation measurements have been averaged over both the trigger and associated particle $\eta$. In order to explore the possible pseudorapidity dependence of the long-range correlations in asymmetric pPb collisions, a new analysis of two-particle correlations with trigger particles at various fixed eta locations is presented. The data were collected during the 2013 LHC pPb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV by the CMS experiment, with a wide eta coverage of -2.4<$\eta$<2.4. The near-side $\Delta$$\eta$ correlations are decomposed into short-range (jet) and long-range components. The away-side long-range correlations in central collisions are also studied by subtracting back-to-back jet contributions, modeled by the away-side correlations from peripheral collisions after accounting for the biases introduced by the multiplicity classification. The long-range correlations are found to be dependent on pseudorapidity. The observed pseudo-rapidity dependence may potentially discriminate theoretical models for long-range two-particle correlations observed in pPb collisions.

Speaker:
Lingshan Xu
(Purdue University (US))

Slides

14:40

Long-range angular correlations at the LHC with ALICE20m

The observation of long-range correlations on the near- and away-side (also known as the double-ridge) in high-multiplicity p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV and its similarity to Pb-Pb collisions remains one of the open questions from the p-Pb run at the Large Hadron Collider. It has been attributed to mechanisms that involve initial-state effects, such as gluon saturation and colour connections forming along the longitudinal direction, and final-state effects, such as parton-induced interactions and collective effects developing in a high-density system possibly formed in these collisions. In order to understand the nature of this double-ridge structure the two-particle correlation analysis has been extended to identified particles. The observed mass dependence in p-Pb resembles qualitative expectations from hydrodynamics, and is also observed in Pb-Pb collisions. A study of correlations at forward rapidity probes the low-x regime of the nucleus, where saturation effects are expected to become stronger. The possibility of accessing this regime using the ALICE forward muon detector is explored. In addition, a possible ridge signal within the ALICE acceptance in pp collisions $\sqrt{s} = 7$ TeV is also investigated.

Speaker:
Leonardo Milano
(CERN)

Slides

15:00

Measurement of the long-range pseudorapidity correlations and associated Fourier harmonics in 5.02 TeV proton-lead collisions with the ATLAS detector20m

Detailed measurement of the Fourier harmonics ($v_n$) associated with the
azimuthal modulation of two-particle correlation structures over
$-5 < \delta\eta < 5$ in 31 nb$^{-1}$ p + Pb collisions are presented. The $v_n$
results are presented as a function of $p_T$, \eta, and event activity
characterized by the number of reconstructed tracks in $-2.5 < \eta < 2.5$,
and the total transverse energy on the Pb-going side ($3.2 < \eta < 4.9$).
The elliptic, triangular, and quadrangular coefficients, $v_2$, $v_3$ and
$v_4$, are extracted for $0.5 < p_T < 15$ GeV, significantly extending the
previous measurements. The v_n values are found to reach a maximum
around 3-5 GeV and then decrease to a finite positive values at $p_T > 10$
GeV, similar to the behavior seen in Pb+Pb collisions. Evidence for
rapidity-even dipolar flow $v_1$ is also observed, further supporting a
collective origin of the long-range two-particle correlations. The first
measurement of the eta dependence of these correlations suggests that
the $v_2$ values are smaller in the proton-going side than those in the
Pb-going side. Finally $v_n$ results are also extracted with four-particle
cumulant method and compared with those obtained with two-particle
correlation method. These results provide new important insights on the
physics underlying the long-range pseudorapidity correlations.

Speaker:
Sooraj Krishnan Radhakrishnan
(State University of New York (US))

Slides

15:20

Long range rapidity correlations and $v_2$ of identified particles in $d$$+$Au collisions20m

Traditionally $p(d)$$+$A collisions at RHIC and the LHC were considered as
a tool to study cold nuclear matter effects. Production of the hot and
dense medium in such collisions was not expected. However recent
measurements has challenged this assumption with the observation of
long-range correlations in angular distributions of hadron pairs
with low transverse momentum. The observed modulations are very
similar to those previously seen in A$+$A collisions which are widely
thought to arise from hydrodynamic flow. The same hydrodynamic models
used in heavy ion collisions have been successful in describing
the $p(d)$$+$A results. However the long-range correlations observed
in $p(d)$$+$A collisions can also be qualitatively described within
the Color Glass Condensate models.
In this talk we present new PHENIX results for azimuthal
angular correlations between charged hadrons measured at mid-rapidity
($|\eta|<0.35$) and energy deposited in calorimeter towers in the
Au-going direction at large rapidity ($-3.7<\eta<-3.1$) in central
$d$$+$Au collisions at $\sqrt{s_{NN}} = 200$~GeV. We report the first
direct evidence for enhanced near-side angular correlations across
$|\Delta\eta| > 2.75$ at RHIC. We also present the first measurement
of $v_2$ for identified charged pions and (anti-)protons in $d$$+$Au
at RHIC, and observe a mass-ordering pattern similar to that seen in
A$+$A collisions.

Speaker:
Drshengli huang
(PHENIX Collaboration)

Slides

15:40

Studies of two-particle correlations with identified $\pi^0$, $K^0_s$ and Lambdas in pPb and PbPb collisions with CMS20m

Observation of a long-range near-side two-particle correlation (known as the "Ridge") in high-multiplicity pp and pPb collisions opened up new opportunities of exploring novel QCD dynamics in small collision systems. To further investigate the origin of this phenomenon, new measurements of two-particle correlations with identified $\pi^0$, $K^0_s$ and Lambda trigger particles in 5.02 TeV pPb and 2.76 TeV PbPb collisions are presented. One unique feature of this analysis is the implementation of a high-multiplicity trigger during the 2013 LHC pPb run, which enables the correlation studies to be performed up to a multiplicity range that is comparable to mid-central PbPb collisions at 2.76 TeV. The $K^0_s$ and Lambdas are cleanly reconstructed via their secondary decay vertices over a wide pseudorapidity and transverse momentum range 0.2 $< p_T <$ 6 GeV/c. Neutral pions are reconstructed through the decay channel of two photons in the $p_T$ range of 0.7-5.0 GeV/c. The second-order ($v_2$) and third-order ($v_3$) anisotropy harmonics of $\pi^0$, $K^0_s$ and Lambda are extracted from long-range correlations as a function of particle multiplicity and $p_T$. The wide $p_T$ coverage and rich sample of high multiplicity pPb events allow: (1) a precise examination of the mass ordering effect of $v_n$ at low $p_T$ as predicted by hydrodynamics for a collectively expanding medium; (2) exploration of possible constituent quark number scaling of $v_2$ and $v_3$ between mesons and baryons as was observed in high-energy nucleus-nucleus collisions.

The study of charmonium production, bound states of c and $\bar{c}$ quarks, is an intense research activity, both experimentally and theoretically. The peculiar properties of some of the charmonium states, like their small size (< 1 fm) and strong binding energy (several hundred MeV), make them ideal probes of the strongly interacting matter, the so-called Quark-Gluon Plasma (QGP), produced in high-energy heavy-ion collisions.
ALICE is dedicated to the study of QGP properties in heavy-ion collisions at the LHC. A suppression of the J/$\psi$ has been found in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV, with respect to the J/$\psi$ measured in pp collisions at the same center-of-mass energy. At the beginning of 2013, p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV have been studied at the LHC, in order to measure the effects related to cold nuclear matter, which, for charmonia, include gluon shadowing (or gluon saturation), energy loss and nuclear absorption. The study of these effects in p-Pb collisions is important in order to be able to disentangle hot and cold nuclear matter effects in Pb-Pb collisions.
The obtained results on the J/$\psi$ production and nuclear modification factor as a function of rapidity or transverse momentum in p-Pb collisions, will be presented and compared to theoretical models. The rapidity ranges considered will include forward and backward rapidity (dimuon decay channel) and mid rapidity (dielectron decay channel). Likewise, a discussion on the forward-to-backward ratios will be held. First results on the dependence of the J/$\psi$ yields and its mean transverse momentum on the charged particle multiplicity will be also presented and discussed.

Z Boson Production in p+Pb Collisions measured by the ATLAS Experiment20m

The measurement of Z bosons in heavy ion collisions is an excellent tool for probing the nucleus at the partonic level. The inclusive yield provides a stringent test of binary collision scaling. Recent ATLAS results demonstrate such scaling in Pb+Pb collisions. The 2013 p+Pb physics run at the LHC providing more than 30 $nb^-1$ of collisions
at an energy of $\sqrt{s_{NN}}$ = 5.02 TeV has made a detailed study of Z boson production in proton+nucleus interactions possible for the first time. These data may confirm binary scaling in the p-Pb system and help clarify the present ambiguity of centrality classifications in proton+nucleus collisions. Further, the momentum and rapidity differential yields of Z bosons allow the detection of any modification of the initial state present in such collisions.

Speaker:
Zvi Citron
(Weizmann Institute of Science (IL))

Slides

15:00

The fate of the weakly bound $\psi'$ in $p$$+$$p$, $d$$+$Au, A$+$A collisions20m

We present new results of a completed analysis from PHENIX of $\psi'$
modification at midrapidity in 200~GeV $d$$+$Au collisions. Strong
differential suppression of the $\psi'$ relative to the $J/\psi$ is
observed. This has also been reported recently by ALICE at forward and
backward rapidity in 5.0~TeV $p$$+$Pb collisions. In all cases the
differential suppression is too strong to be explained by nuclear
breakup effects, due to the short nuclear crossing times. Given the
observation of long range correlations in $p(d)$$+$A collisions at LHC
and RHIC, consistent with hot matter effects, these observations raise
very interesting questions about the mechanism of $\psi'$ suppression
when it is produced in a nuclear target.
In 2012, the PHENIX Collaboration installed the FVTX, a Silicon
Tracker that precisely measures the pair opening angle prior to any
multiple scattering in the muon arm absorber and thus provides an
improved dimuon mass resolution. The FVTX also allows the $\psi'$ to
be separated from the $J/\psi$ at forward and backward rapidity.
During the 2012 data taking run, the PHENIX Collaboration collected a
high statistics data sample of $p$$+$$p$ and Cu$+$Au collisions. We
present new results on the $\psi'$ from this dataset.

Speaker:
J. Matthew Durham
(Los Alamos National Laboratory)

Slides

15:20

Inclusive $\psi$(2S) production at forward rapidity in p-Pb collisions with ALICE at the LHC20m

Charmonium states play a relevant role as probes of the phase transition
between hadronic and deconfined matter. According to the color-screening model,
the in-medium dissociation probability of such states should provide an estimate
of the initial temperature.
In nucleus-nucleus collisions, the more loosely bound excited states, as the $\psi(2{\rm S})$,
are expected to melt at lower temperatures than the ground state (J/$\psi$).
In proton-nucleus collisions at LHC energies, the charmonium formation time is larger than the
time spent by the ccbar pair traversing the nucleus. Therefore, the cold nuclear matter
is expected to affect in a rather similar way the J/$\psi$ and $\psi(2{\rm S})$.
ALICE results on the inclusive $\psi(2{\rm S})$ production at forward rapidities ($2.5 < y < 4$), will
be presented. Final results on the $\psi(2{\rm S})$/J/$\psi$ ratio in Pb-Pb collisions at
$\sqrt{s_{\rm NN}} = 2.76$ TeV will be shown and compared to the corresponding pp measurement.
Results on the $\psi(2{\rm S})$ production in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV
will be also discussed. We observe an unexpected suppression of the $\psi(2{\rm S})$ yield, with respect to
the J/$\psi$ one, which is difficult to reconcile with the presence of cold nuclear matter effects alone.
To provide further insight on this observation, a differential study of the
$\psi(2{\rm S})$ suppression, as a function of transverse momentum and
centrality will be presented. Finally, ALICE $\psi(2{\rm S})$ results will be compared with theoretical models
and with results by other experiments.

Among quantities playing a central role in the theoretical interpretation of
heavy ion collision experiments at RHIC and LHC are so-called transport
coefficients. Out of those heavy quark diffusion coefficents play an important
role e.g. for the analysis of the quenching of jets containing
$c$ or $b$ quarks ($D$ or $B$ mesons) as observed at RHIC and LHC.
We report on a lattice investigation of heavy quark momentum diffusion within
pure SU(3) plasma above the deconfinement transition, with the quarks treated
to leading order in the heavy mass expansion. We measure the relevant
"colour-electric" Euclidean correlator and based on several lattice spacings
perform the continuum extrapolation. This extends our previous study [1,2] progressing towards a removal of lattice artifacts and a physical
interpretation of the results.
We find that the correlation function clearly exceeds its
perturbative counterpart which suggests that at temperatures just above the
critical one, non-perturbative interactions felt by the heavy quarks are
stronger than within the weak-coupling expansion. Our results will be
compared to heavy quark diffusion coefficients [3] obtained from
charmonium vector correlation functions.
[1] A. Francis, O. Kaczmarek, M. Laine, M. Müller, T. Neuhaus and H. Ohno,
"Towards the continuum limit in transport coefficient computations",
arXiv:1311.3759.
[2] A. Francis, O. Kaczmarek, M. Laine and J. Langelage,
"Towards a non-perturbative measurement of the heavy quark momentum diffusion coefficient", arXiv:1109.3941.
[3] H.T. Ding, A. Francis, O. Kaczmarek, F. Karsch, H. Satz and W. Soeldner,
"Charmonium properties in hot quenched lattice QCD", Phys.Rev.D86 (2012) 014509, arXiv:1204.4945.

Speaker:
DrOlaf Kaczmarek
(University of Bielefeld)

Slides

14:20
→
16:00

Jets: 3titanium

titanium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
James Nagle
(Unknown)

announcement

14:20

Measurement of hadron composition in charged jets from pp collisions with the ALICE experiment20m

Jets are defined in QCD as cascades of consecutive emission of partons from an initial hard scattering. The process of parton showering and subsequent hadronisation is broadly known as fragmentation. Identified particles in the final state provide an enhanced sensitivity to the flavor dependence of fragmentation.
ALICE at the CERN LHC is a general-purpose heavy ion experiment designed to study the physics of strongly interacting matter. It provides excellent tracking and particle identification. Charged pions, kaons and (anti-)protons are identified using the TPC specific energy loss (d$E$/d$x$) in the momentum range up to about 40 GeV/$c$. In this talk we present novel measurements of hadron composition ($\pi$/K/p) of charged jets from pp collisions at $\sqrt{\rm s} = 7$ TeV. The results are compared to model calculations and the implications for identified hadron fragmentation functions are discussed.

Speaker:
Xianguo Lu
(Ruprecht-Karls-Universitaet Heidelberg (DE))

Slides

14:40

Jet fragmentation in lead-lead collisions at 2.76 TeV using the ATLAS detector at LHC20m

Measurements of charged particle fragmentation functions of jets
produced in ultra-relativistic nuclear collisions are expected to
provide insight on the modification of parton showers in the hot and
dense medium created in the collisions. ATLAS has measured jets at
sqrt{sNN}=2.76 TeV in Pb+Pb collisions using data collected during
2011 run and in p+p collisions using 2013 run. Jets were reconstructed
using the anti-kt algorithm with distance parameter values R=0.2, 0.3,
and 0.4. Distributions of charged particle transverse momentum and
longitudinal momentum fraction are reported for seven bins in
collision centrality. The ratios of fragmentation distributions with
respect to the p+p reference fragmentation functions are
evaluated. The jet structure is further investigated in terms of
correlations of an angular position and momenta of a particle within
jet.

Speaker:
Martin Spousta
(Columbia University and Charles University)

Slides

15:00

Neutral meson production in pp and Pb-Pb collisions measured by ALICE at LHC20m

The ALICE experiment at LHC performs measurements of neutral meson
inclusive spectra in mid-rapidity
in a wide $p_{\rm T}$ range in pp,
p-Pb and Pb-Pb collisions, as well as correlations between
leading
$\pi^0$ and charged hadrons. Neutral mesons $\pi^0$, $\eta$, $\omega$
are reconstructed via
complementary methods, using the ALICE
electromagnetic calorimeters and by the central tracking
system
identifying photons converted to $e^+e^-$ pairs in the material of the
inner barrel detectors.
Measurements of neutral meson spectra in pp
collisions at energies $\sqrt{s}$ = 0.9, 2.76, 7 TeV provide
valuable
data for pQCD calculations and allow to study scaling properties of
hadron production at the
LHC energies. The study of neutral meson
production in p-Pb collisions at $\sqrt{s} = 5.02$ TeV is of
importance
to confirm that the strong suppresion observed in central Pb-Pb
collisions is a final-state
effect of the produced dense medium.
The
nuclear modification factor $R_{\rm AA}$ of the $\pi^0$ production in
Pb-Pb collisions at
$\sqrt{s_{\rm NN}}$ = 2.76 TeV at different
collision centralities shows a clear pattern of strong
suppression in
a hot QCD medium with respect to pp collisions. We shall also present
the current status
of correlation measurements between $\pi^0$ or
isolated photons triggered by the electromagnetic calorimeter
EMCAL,
and charged hadrons detected in the central tracker.

Production of strange particles in charged jets and underlying event in p--Pb and Pb--Pb collisions with ALICE20m

Properties of the hot and dense strongly interacting matter created in
ultra-relativistic heavy-ion collisions can be studied using jets.
Hadronization processes occurring in jets are expected to be modified by
the interaction of partons with the medium.
At intermediate $p_{\rm T}$, a strong increase of the baryon/meson ratio
is observed for inclusive light particles produced in heavy-ion
collisions when compared to the ratio measured in proton-proton
collisions. Production by fragmentation cannot explain this phenomenon and
other hadronization mechanisms, like coalescence or parton recombination,
have been proposed instead. Measurements of spectra of identified
particles produced in jets in heavy-ion collisions will provide further
important insights into the interplay of hadronization processes which
participate in the jet fragmentation in a medium dominated by the strong
interaction under high temperatures and high energy densities.
In this talk, we present the first measurements of the $p_{\rm T}$ spectra
of $\Lambda$ and $\overline{\Lambda}$ baryons and $\rm{K_s^0}$ mesons
produced in association with charged jets in Pb-Pb collisions at
$\sqrt{s_{\rm NN}}=2.76$ TeV and p-Pb collisions at $\sqrt{s_{\rm
NN}}=5.02$ TeV measured by ALICE at the LHC, exploiting the excellent
particle identification capabilities of this experiment. Baryon/meson
ratios of the spectra of strange particles associated with jets are
studied as a function of centrality and are compared to the ratios
obtained for inclusive particles and for particles coming from the
underlying event

Speaker:
Xiaoming Zhang
(Lawrence Berkeley National Lab. (US))

Slides

15:40

Quantifying jet modification as a function of energy lost and jet mass depletion20m

Jet modification measurements to date are carried out by comparing a surviving jet, exiting a dense medium, with a vacuum (unmodified) jet at the same energy. We propose an extension to classify jet modification in heavy-ion collisions by also including the jet mass. The mass of a jet, as measured by jet reconstruction algorithms, is intimately connected to the jet's virtuality (or scale), which in turn has a considerable effect on such observables as the fragmentation function and jet shape observables. The leading hard parton, propagating through a dense medium tends to experience substantial virtuality (or mass) depletion along with energy loss, and thus accurate comparisons between surviving jets and jets produced in p-p collisions should take these effects into account. Using the event generator PYTHIA, we show the close relationship between the actual jet mass and that after applying a jet reconstruction algorithm. Using the in-medium event generator MATTER++, we demonstrate the clear difference between the mass of a surviving parton exiting a dense medium and a parton with a similar energy formed in a hard p-p event. Effects of this difference in jet mass on the ratio of fragmentation functions and jet shapes are also calculated.

Speaker:
Abhijit Majumder
(Wayne state university)

Slides

14:20
→
16:00

QCD phase diagram: 2helium

helium

darmstadtium

Schlossgraben 1
64283 Darmstadt
Germany

Convener:
Helen Louise Caines
(Yale University (US))

announcement

14:20

Lattice QCD based equation of state at finite baryon density20m

The effects of non-zero baryon density are expected to become
important in hydrodynamic modeling of heavy collisions below the
highest energy at RHIC. Recent calculations in effective models and in
QCD using Dyson Schwinger equation suggest that the transition in QCD
remains a crossover up to baryon chemical potentials of about 800MeV [1].
If so, the equation of state relevant for hydrodynamic models can be
calculated on the lattice using Taylor expansion. However, except for
the coefficients of the lowest order, there are large cutoff effects
in present lattice calculations for non-zero chemical potentials.
To extend our previous parametrization of the equation of state [2] to
finite baryon density, we employ the continuum extrapolated lattice
QCD data on Taylor expansion coefficients in order two [3], and
complement them with coefficients in order four and six evaluated
using p4 action [4]. To avoid large cutoff efects these coefficients
are smoothly matched to those of hadron resonance gas at low
temperature. Some preliminary results were reported in [5]. We also
show how the hydrodynamical evolution is affected by this equation of
state in the energy range relevant for SPS and the RHIC energy scan.
[1] T.K. Herbst et al, Phys. Lett. B696 (2011);
C.S. Fischer et al, Phys. Lett. B702 (2011)
[2] P.Huovinen and P.Petreczky, Nucl.Phys. A837 (2010) 26
[3] S. Borsanyi et al, JHEP 1208 (2012) 053;
A. Bazavov et al, Phys. Rev. D86 (2012) 034509
[4] M. Cheng et al, Phys. Rev. D79 (2009) 074505;
C Miao and C. Schmidt, PoS LATTICE2008 (2008) 172
[5] P. Huovinen, P. Petreczky and C. Schmidt,
Central Eur. J. Phys. 10, (2012) 1385

Speaker:
Pasi Huovinen
(Johann Wolfgang Goethe-Universität)

Slides

14:40

Locating the CEP20m

I review resent results on the chiral and deconfinement
transitions of QCD and the associated phase diagram obtained
from a combination of lattice results with the framework
of Dyson-Schwinger equations. At zero chemical potential we
find excellent agreement with existing lattice results. We
discuss the potential location of the critical endpoint for
Nf=2+1 and Nf=2+1+1 flavors and present first results for the
Polyakov potential at finite chemical potential.

Speaker:
Prof.Christian Fischer
(JLU Giessen)

Slides

15:00

PHENIX beam energy scan results20m

The Beam Energy Scan (BES) program at RHIC has shown the flexibility
to vary the beam energy per nucleon by more than an order of
magnitude, down to the equivalent $\sqrt{s_{NN}}$ of SPS fixed-target
collisions and below. This allows the RHIC experiments to
systematically track the evolution of excited nuclear matter as it
crosses the QGP transition, and to explore new physics at significant
net baryon density such as the possibility of a QCD critical point at
high $\mu_B$. We present new results from PHENIX on the beam-energy
dependence of observables including hydrodynamic flow parameters, 3D
HBT source shapes, and global multiplicity and $E_T$ production. We
also discuss plans to utilize the upcoming BES-II running period at
RHIC.

Speaker:
DrRon Soltz
(Lawrence Livermore Nat. Laboratory (US))

Slides

15:20

Reviewing hadron production in the SIS energy regime using new HADES Au+Au data20m

Data on particle production in heavy ion collisions in the energy regime of 1-2 A GeV have been collected over almost three decades now. As most of the newly created hadrons are produced below or slightly above their free NN-thresholds, data are usually interpreted with the help of phenomenological models, rather than comparing to elementary reference measurements. Driven by advance in detector technology, more and more rare and penetrating probes have become accessible, and still keep challenging our knowledge about the properties of the created system and its dynamical evolution.
The recently collected HADES data from Au+Au collisions at 1.23 A GeV represents in this energy regime the most advanced sample of heavy ion collisions in terms of precision and statistics (7*10$^{9}$ collected events). Using the yields and spectra of reconstructed hadrons ($\pi^{+-}, K^{+-},K^{0}_{s}, \Lambda$) provides therefore the optimal bases to test state of the art models and to question the extent of our present understanding of hadron production.
This work has been supported by BMBF (05P12RFGHJ), Helmholtz Alliance EMMI, HIC for FAIR, HGS-HIRe.

Speaker:
DrManuel Lorenz
(GU Frankfurt)

Slides

15:40

Spectral functions from the functional renormalization group20m

We present a new method to obtain real-time quantities
such as spectral functions and transport coefficients
at finite temperature and density using a
non-perturbative Functional Renormalization Group approach [1].
Our method is based on a thermodynamically consistent truncation of the
flow equations for 2-point functions with analytically continued frequency
components in the originally Euclidean external momenta.
We demonstrate the feasibility of our method by calculating the mesonic
spectral functions in the quark-meson model at different temperatures and
values of the quark chemical potential, in particular near the critical endpoint
of the corresponding phase diagram.
[1] Tripolt, Strodthoff, von Smekal, Wambach, Phys. Rev. D 89, 034010 (2014)

Speaker:
Ralf-Arno Tripolt
(TU Darmstadt)

notes

Slides

16:00
→
16:30

Coffee break
30m

16:30
→
18:30

Poster sessionspectrum

spectrum

darmstadtium

Poster session with pretzels, beer, wine, and soft drinks

16:30

$\omega$(782) and $\phi$(1020) Meson Production in the Dielectron Channel in pp Collisions at $\sqrt{s}$ = 7 TeV with ALICE2h

Low-mass dielectrons are an important experimental tool to investigate the properties of the hot and dense medium created in ultrarelativistic heavy-ion collisions. Electrons do not interact strongly, therefore they provide information from all stages of the collision. In particular, a possible restoration of chiral symmetry in the hot and dense medium can be probed with dielectron decays of short-lived hadrons such as $\omega$(782) and $\phi$(1020) mesons, where pp collisions are used as medium-free reference. Furthermore, pp collisions are interesting by themselves to investigate particle production at LHC energies.
In this poster, the status of a measurement of $\omega$(782) and $\phi$(1020) meson production in the $e^{+}e^{-}$- decay channel in pp collisions at $\sqrt{s}$ = 7 TeV with ALICE is presented. The results are compared to measurements in hadronic and $\mu^{+}\mu^{-}$- decay channels.

Speaker:
Mahmut Ozdemir
(Johann-Wolfgang-Goethe Univ. (DE))

Poster

16:30

$\phi$-meson production in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV measured with ALICE at the LHC2h

Particle production in p-Pb collisions, in contrast to pp, is expected
to be sensitive to nuclear effects in the initial state. The role of
the initial and final state effects can be understood from the measurement
of identified particle spectra. One of the key observables to
characterize the hot and dense matter produced in high-energy
collisions is strangeness production. Here we will present the results
on transverse momentum spectra ($p_{\rm T}$)) and integrated yield of
$\phi$-mesons from p-Pb, $\sqrt{s_{\rm NN}}$ = 5.02 TeV
recorded with the ALICE detector at LHC. The results will be
discussed as a function of multiplicity classes.

Speaker:
Ajay Kumar Dash
(Universidade Estadual de Campinas (BR))

Poster

16:30

$\pi^0$ production in $\sqrt{s_{NN}}$=200 GeV Cu+Au Collisions at PHENIX2h

Cu+Au collisions at RHIC generate asymmetric initial geometries and densities in both azimuth and rapidity. High $p_T$ $\pi^0$s produced in $\sqrt{s_{NN}}$ = 200 GeV Cu+Au collisions provide new environments to study parton energy loss in the Quark Gluon Plasma. including very central events where the Cu nucleus is enveloped by the Au nucleus. By measuring $\pi^0$ yields in $\phi$ relative to the reaction plane, we can probe different core-corona regions in these very central events and study the path length dependence of energy loss in various lopsided initial geometries. PHENIX has observed the suppression of $\pi^0$s with respect to reaction plane in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions and found it consistent with a cubic path length dependence suggesting a non-perturbative energy loss model applies. The unique collision geometries available in Cu+Au provide new settings to explore and possibly confirm this path length dependence. The status of the Cu+Au $\pi^0$ analysis will be presented.

Speaker:
Sarah Campbell
(Iowa State University)

Poster

16:30

$\psi$(2S) signal extraction in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC2h

Quarkonium states are important probes to investigate the properties of strongly interacting matter created in ultrarelativistic heavy-ion collisions and to confirm the presence of Quark-Gluon Plasma (QGP). A significant contribution to the observed suppression can also come from cold nuclear matter effects, which can be studied in proton-nucleus collisions. The $\psi(2{\rm S})$ production is studied in pp, p-Pb and Pb-Pb collisions at LHC energies using the ALICE detector, down to zero transverse momentum, in the dimuon decay channel and in the laboratory rapidity range $2.5 < y < 4$. The statistics is limited, with S/B ratios $\leq$ 0.2 (in pp collisions). In this situation, the extraction of the signal from the dimuon invariant mass distribution becomes very delicate, especially when performing differential analyses (e.g., vs. transverse momentum or rapidity). Therefore, the robustness of the $\psi(2{\rm S})$ signal extraction procedure is crucial to extract final physics results. Several approaches have been investigated, and details on the techniques adopted in the different collision systems will be presented.

Speaker:
Marco Leoncino
(University of Turin and INFN (IT))

Poster

16:30

$\rm W^{\pm}$ boson production measurements in p-Pb collisions with ALICE at the LHC2h

At the LHC, electroweak boson production measurements in p-Pb and Pb-Pb collisions are possible thanks to the availability of higher centre of mass energies as well as higher luminosities with respect to other ion accelerator facilities.
From a theoretical point of view, electroweak boson production can be considered to be well understood. $\rm Z^{0}$ and $\rm W^{\pm}$ bosons are produced in initial hard-scattering processes of partons and are not expected to interact with a strongly interacting medium. Therefore, measurements of electroweak bosons in proton-nucleus and nucleus-nucleus collisions represent a standard candle to check the validity of binary scaling and can provide important constraints to the nuclear parton distribution functions. In addition, such measurements could represent an ideal test-bench for luminosity measurements and detector performance studies.
ALICE is the experiment at the LHC designed to investigate the properties of strongly-interacting matter formed in high-energy heavy-ion collisions. At forward rapidities, ALICE is equipped with a muon spectrometer that allows measurements of dimuon decays of quarkonia, muons from heavy-flavour hadron decays and also $\rm W^{\pm}$ bosons in the muon decay channel. Recent results on the $\rm W^{\pm}$ boson measurement at forward and backward rapidities, with respect to the direction of the proton beam, in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV will be presented.

Speaker:
Francesco Bossu
(iThemba Lab. for Accel. Based Sci. (ZA))

Slides

16:30

$\Sigma^0$ and $\overline{\Sigma}^0$ Baryon Production in pp Collisions at $\sqrt{s}$ = 7 TeV with ALICE at the LHC2h

Hyperon production in heavy-ion collisions is a very precious probe to study the properties of the hot dense matter, as it is sensitive to strangeness enhancement, chiral symmetry restoration and parton energy loss. Moreover, it allows to further constrain the chemical freeze-out parameters based on statistical models. The measurement of the full set of hyperons allows to discriminate prompt and decay hyperons, e.g. prompt $\Lambda$ and one from $\Sigma^0$ decay. The ALICE detector provides a unique capability to study the electromagnetic decay of $\Sigma^0$($\overline{\Sigma}^0$) baryon due to the possibility to measure the low energy photons.
The status of the first observation of $\Sigma^0$ and $\overline{\Sigma}^0$(1192 MeV) baryon in pp collisions at $\sqrt{s} = 7$ TeV by ALICE at the LHC is presented. The $\Sigma^0 \to \Lambda + \gamma$ ($\overline{\Sigma}^0 \to \overline{\Lambda} + \gamma$) signal (branching is 100%) is reconstructed through an invariant mass analysis: the decay $\Lambda \to {\rm p} + \pi^-$ ($\overline{\Lambda} \to \overline{\rm p} + \pi^+$) is detected in the central tracking system of ALICE, while the photon is reconstructed via its conversion. The peak position is in agreement with the PDG data and its width is consistent with the results of Monte Carlo simulation. The $\Sigma^0$ ($\overline{\Sigma}^0$) baryon is measured in the transverse momentum range between 1 and 10 GeV/$c$. In addition, an invariant mass peak is reconstructed with the photon detected in the ALICE PHOS calorimeter.

Speaker:
Alexander Borissov
(Pusan National University (KR))

Slides

16:30

$E_T$ distributions in p+p, d+Au and Au+Au at $\sqrt{s_{NN}}=200$ GeV and analysis based on Constituent-Quark-Participants2h

Measurements of mid-rapidity $dE_T/d\eta$ distributions in p+p, d+Au and Au+Au at $\sqrt{s_{NN}}=200$ GeV by PHENIX at RHIC are presented and analyzed in terms of the number of Constituent-Quark participants, $N_{\rm qp}$. This provides a physical way to introduce fluctuations in Glauber Model calculations of p+p collisions, since the spatial distribution of each of the three constituent quarks in a nucleon is generated according to the measured charge distribution of the proton. It had been noted previously that $dN_{\rm ch}/d\eta$ at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV as a function of centrality is not simply proportional to the number of nucleon participants, $N_{\rm part}$, (the Wounded Nucleon Model, WNM)
but is linearly proportional to the number of constituent-quark participants, $N_{\rm qp}$, (the NQP model).
For symmetric systems, the NQP model is identical to the Additive Quark Model (AQM)
used in the 1980's, to explain a similar disagreement of $dE_T/d\eta$ distributions with the Wounded Nucleon Model in $\alpha+\alpha$ relative to p+p collisions at $\sqrt{s_{NN}}=31$ GeV at the CERN-ISR. However, the AQM and NQP models differ for the case of asymmetric systems such as d+Au, where the AQM, which is a color-string model, is effectively proportional only to the number quark-participants in the projectile. The present d+Au data clearly reject the AQM model in favor of the NQP, which is also in excellent agreement with the Au+Au data. The NQP model also explains why the additional contribution proportional the number of binary-collisions, $N_{\rm coll}$, added to $N_{\rm part}$ to parametrize the centrality-dependence of A+A collisions works, but does not imply a hard-scattering component in $E_T$ distributions and thus is no longer in disagreement with lessons learned from measurements of $E_T$ distributions in p+p(${\bar{\rm p}}$) collisions at the CERN SpS, ISR and SpS-Collider.

Speaker:
Michael Tannenbaum
(Brookhaven National Laboratory (US))

16:30

$J/\psi$ in pPb collisions with CMS2h

Charmonia in nucleus-nucleus (A-A) collisions are an important probe to study for understanding the deconfinement in heavy ion collisions at LHC energies. The measurement in proton-lead (p-A) collisions of prompt and non-prompt $J/\psi$ production enables us to investigate nuclear matter effects and therefore, provides a new input to examine the hot-medium effects in A-A collisions, which are still not fully understood. Using CMS, the transverse momentum and rapidity differential cross-sections, and forward to backward ratios of prompt and non-prompt $J/\psi$ in pPb collisions at center of mass energy per nucleon pair = 5.02 TeV will be presented. The dependence of forward to backward ratios with respect to the event characteristics will also be shown.

Speaker:
Songkyo Lee
(Korea University (KR))

Slides

16:30

$J/\psi$ production in minimum bias U+U collisions at $\sqrt{s_{NN}}=193$ GeV in the STAR experiment2h

Suppression of quarkonia production in high energy nuclear collisions relative to proton-proton collisions, due to color screening of the quark-antiquark potential, has been predicted to be a sensitive indicator of the temperature of the created QGP. However, initial state cold nuclear matter effects, production via recombination of quark-antiquark pairs in the QGP and dissociation in hadronic phase could also alter the expected suppression picture. Systematic measurements of the quarkonia production in different colliding systems are hence crucial for disentangling relative contributions of these effects.
At the STAR experiment we can utilize collisions of uranium nuclei to further study the quarkonia suppression pattern. Since the uranium nuclei are non-spherical, we are able to reach higher energy densities in the most central U+U collision compared to Au+Au collisions. In this poster, we will present the transverse momentum spectrum (0<$p_{\rm T}$<6 GeV/c) and nuclear modification factor of $J/\psi$ production, reconstructed at midrapidity via di-electron decay channel, in minimum bias U+U collisions at $\sqrt{s_{NN}}=193$ GeV in the STAR experiment.

Speaker:
Ota Kukral
(Czech Technical University, Prague)

Poster

16:30

$K^{\ast}$(892)$^0$ resonance production with the ALICE experiment at the LHC2h

Short lived resonances are good probes to study the properties of strongly interacting matter produced in high energy heavy ion collisions. In particular, the resonance ${\rm K^{\ast 0}}$ is important because of its very short lifetime which is comparable to that of the fireball. The decay daughters are expected to undergo re-scattering and re-generation processes, which could modify the characteristic properties of ${\rm K^{\ast 0}}$ such as its mass, width and yield at low transverse momentum ($p_{\mathrm{T}}$). In addition, the yield of ${\rm K}^{\ast 0}$ at high ($p_{\mathrm{T}}$) may be suppressed in Pb-Pb relative to pp collisions due to the effect of the hot and dense medium formation. We report the measurement of the ${\rm K}^{\ast 0}$ resonance in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV via its hadronic decay channel $({\rm K}^{\ast 0}) (\overline{\rm K}^{\ast 0}) \rightarrow {\rm K}^{\pm}({\rm K}^{-}\pi^{+}) )$ with the ALICE detector. The centrality dependence of the mass, width, and yield of ${\rm K}^{\ast 0}$ in Pb-Pb collisions is compared to pp results to investigate the role of re-scattering and re-generation. The nuclear modification factor ($R_{\rm CP}$ and $R_{\rm AA}$) will be presented to study the effect of parton energy loss on ${\rm K}^{\ast 0}$ production and compared with other hadrons to understand the effect of baryon-meson separation.

The study of D mesons in proton-nucleus collisions provides insight into the role of cold nuclear matter effects in charm production, such as the modification of parton densities in nuclei and initial-state multiple partonic scattering. The observed modification of the D-meson transverse momentum distributions in central Pb-Pb with respect to pp collisions has been confirmed as due to hot nuclear matter effects, accessing the effects of cold nuclear matter via p-Pb collisions.
ALICE collected data at $\sqrt{s_{\rm NN}}=5.02~\mathrm{TeV}$ during the 2013 LHC p-Pb run. ${\rm D}^0 \to {\rm K}^- \pi^+$ decays and their charge conjugates were reconstructed in the central rapidity region $|y_{{\rm lab}}|<0.8$. The ${\rm D^0}$ production cross section will be presented as a function of transverse momentum and rapidity. The nuclear modification factor in minimum-bias p-Pb collisions will be presented as well and compared with theoretical predictions including nuclear shadowing or saturation effects. Finally, the dependence of ${\rm D^0}$ production on the multiplicity of charged particles produced in the collision will be discussed.

Heavy quarks (charm and beauty) are a powerful probe to investigate the properties of the medium created in heavy-ion collisions. Due to their large mass, heavy quarks are produced as a result of partonic scattering processes with large momentum transfer, occurring in the early stages of the collisions. The produced heavy quarks travel through the medium, experiencing all the stages of its evolution and finally they hadronize inside or outside the medium. The measurement of the charm production cross section in pp collisions provides an interesting insight in QCD processes and the necessary reference for heavy-ion studies.
ALICE (A Large Ion Collider Experiment) is an experiment at the Large Hadron Collider (LHC) designed to carry out comprehensive measurements of the particles produced in high energy nucleus-nucleus collisions, in order to study QCD matter at high temperature and energy density and the transition between confined matter and the Quark-Gluon Plasma (QGP). D mesons are reconstructed through their hadronic decay channels. The detectors used for the D-meson reconstruction and selection are: the Inner Tracking System (ITS), the Time Projection Chamber (TPC) and the Time-of-Flight (TOF). In addition the Electromagnetic Calorimeter (EMCal) was used, with energy threshold ranging from 1.5 to 2 GeV, to trigger on events with a high energy particle, which allows us to have a data sample enriched of events with heavy flavours.
We present the analysis status of the D$^{+}$-meson production in the data sample of pp collisions at $\sqrt{s}$= 8 TeV collected in 2012. D$^{+}$ mesons are reconstructed in the hadronic decay channel D$^{+} \rightarrow {\rm K}^{-}\pi^{+}\pi^{+}$. We focus on the studies of the D$^{+}$ signals obtained from the invariant mass distributions of triplets of tracks originating from secondary vertices displaced from the interaction point and on the performance of the EMCal trigger.

Speaker:
Ankita Sharma
(University of Jammu (IN))

Slides

16:30

A Fixed-Target Program for STAR: Extending the Low Energy Reach of the RHIC Beam Energy Scan2h

The RHIC Beam Energy Scan (BES) was proposed to search for the possible critical point and to study the nature of the phase transition between hadronic and partonic matter. Data from the NA49 experiment at CERN had suggested the onset of deconfinement at a collision energy of 7.7 GeV [1]. Though RHIC has not demonstrated sufficient luminosity to access collisions below 7.7 GeV in collider mode, collisions between beam nuclei and a gold target will allow STAR to study Au+Au collisions at center-of-mass energies of 3.0, 3.5, 4.0, and 4.5 GeV during the BES phase II. A proof-of-principle study, using collisions between beam halo nuclei and the aluminum beam pipe (runs in 2011 and 2012), has been investigated to demonstrate the feasibility of extracting physics from fixed-target collisions at center-of-mass energies below 7.7 GeV. Performance results from this proof-of-principle study will be presented. The gold target was installed for trigger tests in run 14. The first results of these tests will be presented.
[1] Xi (Omega) production in Pb+Pb Collisions at 158 GeV/c, G. Odyniec for the NA49 Collaboration, J. Phys. G, 23, 1827 (1997)

Speaker:
Brooke Haag
(UC Davis)

Slides

16:30

A Muon Detection System for the CBM experiment at FAIR2h

A Muon detection system is under development for the CBM experiment at the upcoming FAIR facility at GSI. By measuring muon pairs from the decay of low-mass vector mesons and charmonium, the Muon Chamber system (MUCH) will substantially contribute to the exploration of the QCD phase diagram at large baryon chemical potentials. The research program includes the search for de-confinement and chiral phase transitions, and for new phases of strongly interacting matter.
The MUCH subsystem is based on a novel concept of segmented absorbers with varying thickness and detector layers sandwiched between them. Detailed simulations have been performed to optimize the material, the thickness and the position of the absorbers, and the granularity of the detectors. The design goal is to simultaneously identify both high and low momentum muons over the full phase space.
A combination of large size GEM chambers and straw tubes will form the tracking detector system in MUCH. The detectors will be read out in a self-triggered mode to handle unprecedented high interaction rates of 10 MHz. Several prototype detectors have been built and tested successfully with X-rays and particle beams using a self-triggering readout electronics. Results of the feasibility studies and of the detector development will be presented.

Speaker:
Anand Kumar Dubey
(Department of Atomic Energy (IN))

Slides

16:30

A new calculation of light quark jet energy loss using the AdS/CFT correspondence2h

Unlike heavy quarks, light quark energy loss in AdS/CFT is surprisingly dependent on both the string initial conditions and the very definition of the jet itself in the gravity theory. In order to more accurately model QCD jet energy loss in AdS/CFT, we more closely match the string initial conditions to those expected from pQCD and simultaneously propose a novel jet prescription in the dual theory. With the new jet prescription, light quark jet energy loss regains the “explosive,” late-time Bragg peak in both static and expanding plasmas. We incorporate the improved AdS/CFT results into a phenomenological energy loss model and compare our predictions to light meson suppression at RHIC and LHC.

Speaker:
Razieh Morad
(University of Cape Town)

Slides

16:30

A New Study of Parton Energy Loss Mechanisms in p+A Collisions at Fermilab E906 Experiment2h

Jet quenching in heavy ion collisions is considered to be one of the important tools to study the QGP properties at RHIC and LHC. However, at present there are several competing models to describe the jet energy loss processes in heavy ion collisions, and current heavy ion data cannot clearly discriminate between them, thus the interpretation of QGP data is very model dependent. High energy p+A collisions may provide control of various cold nuclear matter effects, and with the proper kinematics, provide a clear determination and calibration of various parton energy loss models, thereby helping to improve the calculations for A+A. Past efforts to extract the effects of parton energy loss in p+A resulted in a large uncertainty due to ambiguities from competing effects, such as parton shadowing.
E906/SeaQuest is a new fixed-target dimuon experiment using 120 GeV proton beams from the Fermilab main injector. E906 measures J/Psi and Drell-Yan production in the dimuon channel in p+p and p+A collisions over a wide range of xF, and employs fixed targets of D, C, Fe, and W. The kinematic coverage is ideal for parton energy loss studies for 20~60 GeV “incoming” quarks, and shadowing effects are expected to be minimal. E906 had its first engineering run in early 2012 and successfully observed the J/Psi mass peak in the dimuon channel. E906 is currently taking high statistics data since the beginning of this year. We expect the new data will help clarify the nature of parton energy loss in the nuclear medium. In this talk, we will briefly review the latest progress in parton energy loss study in p(d)+A collisions and present the current status and the prospects from the E906/SeaQuest experiment at Fermilab.

Speaker:
DrMing Liu
(Los Alamos National Laboratory)

16:30

An Analytic Study of the Initial Energy Momentum Tensor in Nuclear Collisions2h

We present an analytic calculation of the initial classical gluon field in high energy collisions of nuclei. Our results are explicit expressions for the components of the event-averaged energy momentum tensor which are valid up yo times $\tau\sim1/Q_s$. In particular we will discuss the early time evolution of the energy density and longitudinal and transverse pressure, and compare to available numerical results. We then demonstrate how both a rapidity-odd and rapidity-even energy flow emerge naturally from the QCD analogues of Faraday's and Gauss' Law. We discuss their phenomenological consequences in terms of initial elliptic flow, global angular momentum and directed flow. We will also briefly mention how an event generator can be built based on these results.

Speaker:
Rainer Fries
(Texas A&M University)

Poster

16:30

An Electron Ion Collider (EIC) Detector Built Around the BaBar Magnet (ePHENIX)2h

As a particular realization of an electron ion collider (EIC), the
eRHIC project envisions the addition of a high intensity polarized
electron beam to the existing RHIC facility, providing $e$$+$$p$ and
$e$$+$A collisions and enabling precision studies of the partonic
structure of hadronic matter. To fully exploit the physics potential
of eRHIC, the PHENIX Collaboration is proposing a detector built upon
sPHENIX, a planned upgrade of the current PHENIX experiment. This new
detector, ePHENIX, uses the sPHENIX superconducting solenoid and
barrel calorimetry and adds to this foundation precision tracking,
particle-identification and calorimetry in the barrel, electron-going
and hadron-going directions, opening a broad range of exciting EIC
physics measurements (see \url{http://arxiv.org/abs/1402.1209}). We
give an overview of ePHENIX detector design and discuss its broad
capabilities for both nucleon structure imaging and high density
nuclear matter studies.

Speaker:
David Morrison
(BNL)

16:30

Analysis of D-h and D-e angular correlations with ALICE, and perspectives for the upgrade2h

In collisions of lead nuclei at the Large Hadron Collider (LHC) at CERN, a state of matter called Quark-Gluon Plasma (QGP) is predicted to be formed, where quarks and gluons are no longer confined into hadrons. Heavy-flavour quarks, i.e., charm and beauty, are effective probes for studying the QGP, as their relatively large mass limits their production predominantly, if not exclusively, to hard scattering processes in the very first moments of the collisions, before the QGP formation. As the quarks propagate through the hot and dense medium created in the Pb-Pb collisions they interact with the medium and lose energy via elastic collisions and gluon radiation.
The study of the modification of the angular correlation between D mesons and charged hadrons, as well as the correlation between D mesons and electrons from heavy-flavour hadron decays in Pb-Pb collisions with respect to pp and p-Pb collisions can provide relevant information on the energy-loss mechanism. This applies in particular to the dependence of the correlation on the path length traversed by the charm quark in the medium, and to possible medium modifications of charm-quark fragmentation and hadronisation. In pp collisions, these measurements can be sensitive to the different production processes of heavy-flavour quarks, e.g., pair production vs. gluon splitting. In this poster, the results of the analysis of azimuthal correlations between D mesons and charged hadrons in pp collisions at $\sqrt{s}=7$ TeV and p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV will be presented. In addition, the prospects for measuring correlations of D mesons and electrons from heavy-flavour hadron decays will be discussed. The performance expected after the upgrade of the ALICE detector during the long shutdown in 2018 will also be shown.

Speaker:
Per-Ivar Lonne
(University of Bergen (NO))

Poster

16:30

Anisotropic flows and the shear viscosity of the QGP within a transport approach with initial state fluctuations.2h

We discuss the build up of elliptic flow and high order harmonics $v_n$ within a transport
approach at fixed shear viscosity to entropy density ratio and with initial state fluctuations.
We show, exploring the $T$ dependence of $\eta/s$, that a study of $v_n$ in a wide $p_T$ range
allows to understand the difference behind the collective flows at LHC respect to RHIC. Furthermore
we present novel results about the impact of $\eta/s$ on the correlations between the initial
space eccentricity $\epsilon_n$ and the final anisotropic flows $v_n$.
In particular we study the effect of a temperature dependent $\eta/s$ at different beam energies
from RHIC for $Au+Au$ at $\sqrt{s}= 62.4, 200$ GeV to LHC energies for $Pb+Pb$ at $\sqrt{s}= 2.76$ TeV.
We find that for the different beam energies considered the suppression of the elliptic flow
due to the viscosity of the medium has different contaminations coming from the hadronic or
QGP phase depending on the average energy of the system.
References
[1] S. Plumari, V. Greco and L.P. Csernai, arXiv:1304.6566 [nucl-th].
[2] M. Ruggieri, F. Scardina, S. Plumari and V. Greco, Phys.Lett. B727 (2013) 177-181.
[3] S. Plumari, A. Puglisi, F. Scardina and V. Greco, Phys.Rev. C86 (2012) 054902.

Applications of Chaos Many-Bode Engine for the analysis of relativistic nuclear collisions at 200 A GeV/c2h

Recently, we proposed a C# code, namely Chaos Many-Body Engine [1,2], for chaos analysis of relativistic many-body systems with reactions. Preliminary tests using a simplified relativistic nuclear collisions model resulted in some encouraging results for describing global physical quantities obtained in C-C collisions at 4.5 A GeV/c in experiments performed at JINR Synchrophasotron (SKM 200 Collaboration) [3]. The code allows introduction of some additional interactions among particles in the participant region, thus improving the description of the particle production in nucleus-nucleus collisions. The code permits, also, the investigation of time evolution of the collisions, from the initial moment up to the freeze-out. The time evolution step can be below 0,1 Fm/c. Using the possibilities for code development, we try to improve the agreement between our code and existing experimental results. Two collisions will be discussed, namely Cu-Cu at maximum BNL energy, and d-Au at the same energy. The code predictions and experimental results improve the agreement when we include more collisions and particle production mechanisms in the participant region. The time evolution of the fireball is well reflected by our code (Fig.1), for an evolution time between 0,1 and 200 Fm/c.
For the time evolution, code hypotheses do not cover all aspects and some behaviors of the experimental results are not completely described. Work is in progress for improving the agreement with the experimental results.
[1]. I.V.Grossu et al. – Comp.Phys.Comm. 179(1-3)(2008)199, 181(8)(2010)1464, 184(4)(2013)1346
[2]. I.V.Grossu et al. – accepted for publication in Comp.Phys.Comm. 185(2014)
[3]. I.V.Grossu et al. – Annual Scientific Session of the Faculty of Physics, University of Bucharest, 2013

Approach to equilibrium: Universal properties in expanding gauge and scalar field theories2h

We show simulation results for longitudinally expanding gauge and scalar field theories as they approach thermal equilibrium. Most remarkably, we find a common nonthermal attractor solution in a characteristic momentum regime. As a consequence, important aspects of the evolution towards equilibrium turn out to be insensitive to the details of the underlying theory.

Speaker:
Kirill Boguslavski
(Heidelberg University)

Poster

16:30

Azimuthal asymmetries in high-energy collisions of protons with holographic shockwaves2h

Large azimuthal quadrupole and octupole asymmetries have recently been found in p+Pb collisions at the LHC. We argue that these might arise from a projectile dipole scattering off randomly shaped intrinsic fluctuations in the target with a size on the order of the dipole. Generic energy-momentum fluctuations generate comparable asymmetries for all multipole moments vn. The holographic description of this process involves the calculation of a light-like Wilson loop in the background of a non-uniform holographic shockwave in the presence of a Neveu-Schwarz 2-form.

It has been known for a long time that neutral-pions dominantly decay into two photons,
which was subsequently understood on a robust theoretical basis after the discovery of chiral anomaly.
A theorem shown in a seminal paper by Adler and Bardeen [1] indicates
that a neutral pion is coupled to only two-photon states without couplings to other multi-photon states.
When chiral anomaly is tied to extremely strong magnetic fields created in ultrarelativistic heavy-ion collisions [2],
we find
that transition between a neutral pion and a photon becomes possible
with one of the two photons replaced by an external magnetic field.
The theorem allows us to obtain the transition amplitude governed by chiral anomaly without theoretical ambiguities.
We discuss attainable signatures of the anomaly-induced transition
between neutral pions and photons in RHIC and LHC experiments.
Although the magnetic fields persist for $1\, {\rm fm}/{\it c}$ or even shorter duration
after the heavy ion collisions,
we still find a photon source having much chance to interact with the magnetic field,
that is, the prompt photon emitted just at the impacts of the collisions.
While the prompt real photons propagate in the magnetic field,
a part of the photons is converted into neutral pions, leaving an reduced amount of photons.
Then, we show that the prompt photons to be measured in the experiments
should have a negative $v_2$ and particular polarizations [3],
since the transition amplitude is azimuthally anisotropic and depends on the photon polarizations
due to a preferred orientation prescribed by the external magnetic fields.
We propose that analyses on those observables should be performed in the future experiments,
which makes the creation of the strong magnetic fields evident,
while major attention has been conventionally paid to the total yield of prompt photons.
We take into account the time dependence of the magnetic fields,
and show the beam energy and impact parameter dependences of
the photon's $v_2$ and polarizations.
This work will provide impacts on elucidating formation of the prompt-photon spectrum
as a penetrating probe from the very early stage,
and thus shed light on an aspect of the early-time dynamics in the heavy-ion collisions.
1. S. Adler and W. Bardeen, Phys. Rev. 182 (1969) 1517-1536.
2. D. E. Kharzeev, L. D. McLerran, and H. J. Warringa, Nucl. Phys. A 803 (2008) 227-253;
V. Skokov, A. Y. Illarionov and V. Toneev, Int. J. Mod. Phys. A 24 (2009) 5925-5932;
A. Bzdak and V. Skokov, Phys. Lett. B 710 (2012) 171-174;
W. T. Deng and X. G. Huang, Phys. Rev. C 85 (2012) 044907.
3. K. Hattori, K. Itakura and S. Ozaki, arXiv:1305.7224 [hep-ph].

Collisions between uranium nuclei have been produced in the Relativistic Heavy Ion Collider and measured in the STAR detector. Due to the prolate deformation of the nuclei, fully overlapping U+U collisions offer the opportunity to produce highly anisotropic participant zones, similar in shape to mid-central Au+Au collisions, but with twice the size. The larger fireball should be characterized by a long time over which it collectively evolves from its non-trivial initial shape to its final one. The final-state anisotropy of zero-spectator collisions in *momentum* space ($v_n$) is under active study. We will present a preliminary analysis of the *coordinate*-space anisotropy, measured via azimuthally-sensitive two-pion interferometry ("HBT") of full-overlap collisions, performed differentially in the reduced flow parameter $q_{2}$ in U+U collisions at$\sqrt{s_{NN}}$ = 193 GeV.

Speaker:
John Campbell
(The Ohio State University)

16:30

Baryon-to-meson ratio of strange particles in near-side and away-side jets in pp collisions with ALICE using azimuthal correlations2h

Two-particle azimuthal correlations are an ideal tool to study high $p_{\rm T}$ parton fragmentation without full jet reconstruction. Enhancements of the azimuthal correlations are seen at $\Delta \varphi = 0$ and $\Delta \varphi = \pi$, corresponding to the near-side and away-side jets, respectively. We present correlations between charged leading particle and associated strange baryons ($\Lambda$) and mesons (${\rm K_s^0}$) in pp collisions at $\sqrt{s}$ = 7 TeV. Associated particle yields in near- and away-side jets, as well as in the underlying event, were extracted in different $p_{\rm T}$ intervals from 1 GeV/$c$ to 6 GeV/$c$. Extracted $\Lambda/{\rm K_s^0}$ in jets and the underlying event were compared to the inclusive $\Lambda/{\rm K_s^0}$ ratio and pQCD-inspired models.

Speaker:
Sandun Pahula Hewage
(University of Houston (US))

16:30

Beam Energy Dependency of Clan Multiplicity at RHIC2h

Negative binomial distribution has been widely used in describing the multiplicity distribution in high energy collisions. The parameters of a negative binomial distribution can be transformed to clan parameters,
namely, the average number of clans and the average number of particles per clan (clan multiplicity) [1]. Clan parameters have been used to identify abnormalities due to a phase transition. In this talk, STAR's measurement of clan multiplicity will be presented for AuAu collisions at center-of-mass energies of 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV per nucleon-nucleon pair. The energy dependence will be studied for events from various centrality classes. The implications of these results to the search for possible signals of a phase transition and/or a critical point will be discussed.
[1] A. Giovanni, L. Van Hove, Z. Phys. C30 391 (1986).

Speaker:
DrAihong Tang
(Brookhaven National Laboratory)

16:30

Beam energy scan using a 3+1D viscous hydro+cascade model2h

Following the BES program at BNL RHIC, we perform a similar collision energy scan using a 3+1D viscous hydrodynamics coupled to the UrQMD hadron cascade. We study how the collision energy affects the bulk observables: rapidity distributions and $m_T$-spectra of identified particles, elliptic flow, directed flow and HBT radii, including azimuthally-sensitive HBT. In our calculations we use an equation of state for finite baryon density and averaged or event-by-event initial conditions from UrQMD.
We show that the final observables are sensitive to the initial state fluctuations and its granularity, as well as to the shear viscosity in the hydrodynamic stage. Fortunately the simultaneous reproduction of rapidity/$m_T$ distributions from NA49 and newer elliptic flow data from STAR can constrain both the granularity of the initial state and shear viscosity in hydrodynamic phase. We also explore the impact of different equations of state on final observables, and the possibility to discriminate between them.

Short range correlations of identified charged hadrons in pp ($\sqrt{s}$ = 0.9, 2.76, and 7 TeV), pPb ($\sqrt{s_{NN}}$ = 5.02 TeV), and peripheral PbPb collisions ($\sqrt{s_{NN}}$ = 2.76 TeV) are studied with the CMS detector at the LHC. Charged pions, kaons, and protons at low $p_T$ and in laboratory pseudorapidity $|\eta| < 1$ are identified via their energy loss in the silicon tracker. The two-particle correlation functions show effects of quantum statistics, Coulomb interaction, and also indicate the role of multi-body resonance decays and mini-jets. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as a function of pair momentum and the charged-particle multiplicity of the event. The extracted radii are in the range 1-5 fm, reaching highest values for very high multiplicity pPb, also for similar multiplicity PbPb collisions, and decrease with increasing $k_{T}$. The dependence of radii on multiplicity and $k_{T}$ largely factorizes and appears to be insensitive to the type of the colliding system and center-of-mass energy.

Speaker:
Ferenc Siklér
(Wigner RCP, Budapest (HU))

Slides

16:30

Bottomonium at finite temperature from lattice QCD2h

I will present some recent results from the FASTSUM collaboration on the bottomonium spectrum at finite temperature from lattice QCD.
From the calculation of the spectral functions using the maximum entropy method we confirm earlier findings on the survival of the ground state S wave states up to at least 2$T_c$ and observe further strong indications of the dissociation of the P wave ground states immediately in the deconfined phase.
In this work we use ensembles with $N_f=2+1$ dynamical quarks and improved lattice parameters.
The heavy quark is treated with a non-relativistic effective theory on the lattice and serves as a probe of the hot medium.
We discuss the reconstruction of the spectral functions from the Euclidean correlation functions.

Speaker:
Tim Harris
(Trinity College, Dublin)

Poster

16:30

Bottomonium melting from a stochastic potential2h

Understanding the suppression patterns of heavy Quarkonium promises valuable insight into the quark-gluon plasma created in relativistic heavy-ion collisions at RHIC and LHC. Here we present simulations of Bottomonium real-time evolution [1] in an idealized, i.e. static, QGP at high temperature, based on the open-quantum systems concept of stochastic potential [2].
If a heavy Quarkonium bound state is submerged in the QGP, it is subject to screening and scattering from the surrounding light partons. Effective field theory tells us that under such circumstances its correlation function obeys a Schrödinger equation with a complex potential V(r).
We interpret the resulting loss of correlations with the initial state, i.e. the presence of Im[V], as decoherence, which is induced by the thermal fluctuations of the medium. To incorporate this phenomenon into the non-relativistic description, we use a purely real potential, whose values are stochastically varied at each time step by purely real noise. It is the spatial noise correlations that are then intimately related to Im[V].
Based on this setup, we discuss the intricate interplay between state mixing and thermal (de-)excitations, which governs the real-time evolution of Bottomonium vacuum initial states, as they propagate in the QGP.
[1] A.R. arXiv:1312.3246 submitted to JHEP
[2] Y.Akamatsu and A.R. Phys.Rev. D85 (2012) 105011

Speaker:
Alexander Rothkopf
(H)

Slides

16:30

Causal hydrodynamic fluctuation and its implementation in full (3+1)-D dissipative hydrodynamic simulation2h

We formulate relativistic fluctuating hydrodynamics with causal hydrodynamic fluctuations and implement them into our dynamical model for more quantitative analysis of the transport coefficients of the matter created in heavy ion collisions.
The hydrodynamic fluctuations are thermal fluctuations arising in the event-by-event hydrodynamic evoluation of the system, and its power spectrum is determined through the fluctuation-dissipation relation. While, the higher harmonics $v_n$ ($n>2$) are systematically observed in RHIC and LHC and attract a lot of theoretical and experimental interests. Initial state fluctuations turned out to be important to explain these higher harmonics through event-by-event hydrodynamic simulations. The event-by-event hydrodynamic fluctuation, although its average is locally zero, also has effects on the higher harmonics and other observables in the same manner as the initial fluctuations which vanish in the averaged picture of the initial condition.
Recently, it is actively discussed to extract the shear viscosity from the experimental observables using hydrodynamic simulations with the initial fluctuations. The initial fluctuations are converted to observables through the response of the matter, which enables us to obtain information on the properties of the matter as well as on the initial state. But, the higher harmonics are created not only by initial state fluctuations, and the other sources of fluctuations such as the hydrodynamic fluctuation also play important roles. Therefore, to extract the quantitative properties of the quark-gluon plasma from experimental data, it is important to properly implement all the sources of fluctuations including hydrodynamic fluctuations in an integrated dynamical model with models of initial states, hydrodynamics of quark-gluon plasma and subsequent hadronic cascades.
First, we formulate relativistic fluctuating hydrodynamics with the hydrodynamic fluctuation \[1\] in the context of the causal dissipative hydrodynamics which are commonly used in dynamical models for heavy-ion collisions. In causal dissipative hydrodynamics, the hydrodynamic fluctuation of the dissipative currents becomes colored noise due to the fluctuation-dissipation relation. But, interestingly, noise turns out to be always white in the differential form of the constitutive equations, which comes from general properties of the response function of the dissipative currents including causality and resulting constraints on the structure of the constitutive equations. Next, we implement the hydrodynamic fluctuations into our integrated dynamical model and investigate the behavior of the hydrodynamic fluctuations in heavy-ion collisions and discuss effects on experimental observables. The effect can be more significant in higher orders of the harmonics $v_n$, and in smaller systems such as peripheral collisions or central pA collisions.
**References**
\[1\] Koichi Murase, Tetsufumi Hirano, arXiv:1304.3243 [nucl-th]
![(2+1)-D example of hydrodynamic fluctuations][2]
[2]: http://tkynt2.phys.s.u-tokyo.ac.jp/~murase/share/murase_qm2014f.gif "hydrodynamic fluctuations"

Speaker:
Koichi Murase
(The University of Tokyo)

Slides

16:30

Cavitation and bulk viscosity2h

It has been show that hydrodynamic models provide an effective, phenomenological description of the QGP. The framework of hydrodynamics allows the occurrence of interesting phenomena like cavitation. Cavitation, in general, is the phase change from the liquid to the gaseous phase caused by a pressure drop.
First, one way of defining cavitation for relativistic hydrodynamics is presented. Afterwards, by using this previously defined concept, it is possible to constrain the maximum value of the bulk viscosity over entropy density $\zeta/s$, a value that is currently not easily accessible by other methods. Although bulk viscosity exists only in non-conformal fluids, this approach can be justified as a small perturbation to a conformal fluid setup. Numerical and analytical methods are discussed, and the results are compared with known cases.

Speaker:
Mathis Habich
(University of Colorado Boulder)

Poster

16:30

Centrality and pseudorapidity dependence of dE$_T$/d$\eta$ in pPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV with CMS2h

High energy proton lead collisions provide a unique tool to study the parton distribution function of nuclei at very low Bjorken x. The production of transverse energy at a given eta is sensitive to the gluon density in the nucleus, and by scanning over a very wide rapidity and centrality range, it is possible to glean information on the spatial and x dependence of the gluon density. The ratio of dE$_{T}$/deta at a given centrality range to the most central range for pPb collisions at center of mass energy per nucleon pair = 5.02 TeV is presented. The centrality dependence of this ratio depends strongly upon eta and also on the eta range used to define centrality. These results are compared to lower energy data and two Monte Carlo simulators, EPOS and AMPT, in order to provide insight into the nuclear wavefunction at low x.

High energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, many of which are expected to have a significant dependence on the impact parameter of the collision, which is related to the collision centrality. We detail a method, employed by PHENIX, for determining centrality classes in $p(d)+A$ collisions via cuts on the produced charge particle multiplicity in the nucleus-going (-3.9<$\eta$<-3.0) direction. Using a Glauber Monte Carlo simulation we are able to map the centrality classes to geometric quantities of interest, along with corresponding systematic uncertainties. Within this framework we calculate the centrality bias-correction factors on the nuclear modification factor $R_{p(d)+A}$ due to correlations between a measured process and the multiplicity in the nucleus-going direction. These bias-correction factors are tested further using the HIJING MC generator, confirming that for $d+$Au collisions at $\sqrt{s_{NN}}=200$ GeV the corrections are small and vary by less than 5% (10%) for hadron production at midrapidty up to $p_{T}$=10(20) GeV/$c$. In contrast, we find that the bias correction factors for $p+$Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV are an order of magnitude larger and exhibit a strong dependence on hadron $p_T$, which likely is due to the larger effect of multiparton interactions.

Speaker:
DrDarren McGlinchey
(University of Colorado)

Slides

16:30

Centrality dependence of the J/$\psi$ production in p-Pb collisions with ALICE at the LHC2h

The study of proton-nucleus collision at LHC energies represents an important step in Quark-Gluon Plasma related studies, allowing a quantitative evaluation of cold nuclear matter effects on various observables.
The ALICE Collaboration is carrying out a comprehensive study on charmonium production in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV in the dimuon decay channel. The analysis of the centrality dependence of the J/$\psi$ production is now in progress. Various centrality-related observables are being investigated, and their use in the charmonium analysis is being evaluated.
In this poster, we will discuss the present status of the study of the centrality dependence of the J/$\psi$ production in p-Pb collisions, including an estimate of the $\langle p_{\rm} \rangle$ evolution with centrality.

Speaker:
Igor Lakomov
(Universite de Paris-Sud 11 (FR))

Poster

16:30

Centrality Detector for Collider-based Heavy Ion Experiments2h

Parameters of the initial state of the heavy-ion (HI) interaction are commonly denoted by the term “centrality”. Centrality includes the impact parameter of the interaction, amount of interacting material and relative orientation of colliding nuclei. Unfortunately, none of these parameters can be directly measured. In all currently operating and planned HI experiments centrality is measured indirectly, using particles produced in the HI interactions, usually at high-rapidity. That requires assumptions about the high-rapidity particle production mechanisms that are not very well studied, and also requires a model relating produced particles to the initial state geometry, the Glauber model. These two assumptions lead to significant systematic uncertainties in centrality determination. Further, use of produced particles is affected by the correlations between the centrality determination rapidity and the rest of the detector coverage, where the physics measurements are done. This, in turn, requires additional corrections resulting in additional systematic uncertainties. Recent results from the LHC experiments reveal the importance of the long-range rapidity correlations in HI interactions. The proton-lead results also demonstrate that the Glauber model itself may require further adjustments.
In collider-based HI experiments there is a unique possibility to measure centrality parameters by registering spectator fragments remaining from the collision on both sides. Spectator fragmentation mechanism is decoupled from particle production mechanism. This approach does not require Glauber model as spectators and participants are related via the total number of nucleons in the colliding species. Spectators continue flying along the direction of the colliding beams retaining practically unmodified longitudinal momentum, however their mass-to-charge ratio is typically lower than that of the colliding species.
We propose a concept of the Centrality Detector, which measures masses of most of the fragments by measuring their deflection in the magnetic field of the collider elements and their charges. The field, and a set of detectors integrated in the structure of collider rings act as a very precise mass-spectrometer for such fragments. First calculations based on the DPMJet generator show that the Centrality Detector can provide better accuracy than currently used methods. Main factors affecting its performance will be discussed in the presentation.

Speaker:
Alexander Milov
(Weizmann Institute of Science (IL))

Slides

16:30

Charge dependent elliptic flow from anomalous hydrodynamics2h

Anomaly-induced transport effects, like the chiral magnetic effect or the chiral separation effect, have recently attracted much attention. These effects represent the existence of dissipationless vector and axial currents along the magnetic field and are expected to occur in ultra-relativistic heavy-ion collisions. It has been pointed out that the coupling between the chiral magnetic effect and the chiral separation effect provokes a novel type of gapless collective excitation in the plasma, called chiral magnetic wave (CMW).
The experimental search for anomaly-induced transports in heavy-ion collisions is now ongoing. Since the CMW leads to an electric charge quadrupole deformation in the quark-gluon plasma (QGP) created in heavy-ion collisions, the elliptic flow parameter $v_2$ would be charge-dependent, which can be considered as a signal of anomalous transports [1]. The STAR Collaboration observed such a charge dependent elliptic flow for pions $\Delta v_2 (\pi^\pm)$ [2]. This result seems to be consistent with the prediction from a simple model [1], in which propagation of non-interacting waves under spatially and temporally uniform temperature and homogeneous magnetic field is considered. However, since the QGP created in heavy-ion collisions is drastically expanding, it is necessary to describe the space-time evolution of the QGP together with that of electromagnetic fields in order to assess the contribution from anomalous transports.
In this study, we numerically solve anomalous hydrodynamic equations and apply it to the dynamics of heavy-ion collisions [3]. We develop a numerical code which is applicable to the description of the QGP under arbitrary external electromagnetic fields. We describe the propagation of the CMW in the expanding QGP under spatially and temporally inhomogeneous external electromagnetic fields. We analyze the charge-dependent elliptic flow $v_2^\pm$ and discuss possible implications for experimental observations of anomalous transport effects.
**References:**
[1] Y. Burnier, D. E. Kharzeev, J. Liao, and H. -U. Yee, Phys. Rev. Lett. 107, 052303 (2011)
[2] G. Wang [STAR Collaboration], Nucl. Phys. A904-905 2013, 248c (2013)
[3] M.Hongo, Y. Hirono, T. Hirano, [arXiv: 1309.2823]

We investigate the effect of the Coulomb field of the spectator matter on the directed and elliptic flow of charged pions. By means of a numerical Monte Carlo simulation, we find that the spectator charge induces sizeable values of directed flow. At beam and target rapidities, these can reach $v_1$=0.2 which is comparable to values reported by the WA98 collaboration in the corresponding kinematical range [1].
This effect is opposite for positive and negative pions, resulting in a *charge splitting of directed flow*. In the range of lower RHIC and SPS energies, the charge splitting extends down to midrapidity where our predicted values are in good agreement with very recent measurements reported by the STAR collaboration [2]. This effect appears to be strongly sensitive to the position of the pion formation zone with respect to the spectator system. Therefore, it provides *new, independent information* on the expansion of participant matter in the course of the collision.
By comparing the results of our predictions with the STAR and WA98 data, we investigate the *geometrical features* characterizing pions at freeze-out as they appear from our study of electromagnetic effects. We discuss the possibility to use the spectator-induced electromagnetic interaction as a new source of information on the space-time evolution of particle production at high energies.
Finally, for the first time, we present our new results on the *charge splitting of elliptic flow* which we discuss in the context of measurements reported by the STAR collaboration [3]. Additionally, we stress the complementarity of our study to the very recent analysis by Gursoy, Kharzeev and Rajagopal [4].
Most of this work was previously published in Ref. [5].
References:
[1] H. Schlagheck (WA98 Collaboration), Nucl. Phys. A **663**, 725 (2000).
[2] L. Adamczyk *et al.* (STAR Collaboration), arXiv:1401.3043 [nucl-ex].
[3] L. Adamczyk *et al.* (STAR Collaboration), Phys. Rev. Lett. **110**, 142301 (2013), arXiv:1301.2347 [nucl-ex].
[4] U. Gursoy, D. Kharzeev and K. Rajagopal, arXiv:1401.3805 [hep-ph].
[5] A. Rybicki and A. Szczurek, Phys. Rev. C **87**, 054909 (2013), arXiv:1303.7354 [nucl-th].

Charged Hadron Suppression at High pT in Au+Au Collisions at 200 GeV2h

The nuclear modification factor of single hadrons still provides one of the strongest constraints on energy loss mechanisms in the Quark-Gluon Plasma. Currently the best measurement at RHIC is made with neutral pions. Charged hadrons have independent sources of systematic uncertainty and thus can provide additional constraints. In PHENIX, the background from conversions and weak decays mimicking high $p_{T}$ particles has limited the measurement of charged hadron to $p_{T} < 10$ GeV/$c$. The recently installed silicon vertex tracker (VTX) will be used to reject this background allowing the measurement of charged hadrons out to $20$ GeV/$c$. The VTX is capable of performing precision tracking measurements of distance of closest approach to the primary vertex (DCA). Conversions and weak decays do not originate from the primary vertex and are vetoed with the VTX by rejecting tracks with large DCA. The status of high $p_{T}$ charged tracking and associated nuclear modification factors will be reported.

Speaker:
MrJason Bryslawskyj
(CUNY Baruch)

Slides

16:30

Charged jets in p-Pb collisions with the ALICE detector2h

Highly energetic jets are sensitive probes for the kinematics and the topology of high energy collisions. They are produced in an early stage of the collision from hard scattered partons that hadronize and eventually form jets as a spray of charged and neutral particles.
The measurement in p-Pb provides an important reference to study the effects of cold nuclear matter on jet production and hadronization. This is possible because the formation of a hot and dense medium like in Pb-Pb is not expected. Besides the comparison to Pb-Pb collisions, p-Pb analyses can also be an important constraint for the nuclear parton density functions providing information about the nuclear environment.
In terms of analysis techniques, the exact evaluation of the background from the underlying event is an important ingredient. It is much smaller than in Pb-Pb so that the methods for background estimation need to be refined.
Our jet analysis of p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV is performed on data taken by the ALICE detector at the LHC in the beginning of 2013. The focus of our analysis lies on the jet spectra and their comparison to the spectra from pp collisions, including results depending on the multiplicity or centrality classes given in p-Pb collisions. For this analysis various estimates for the background and its fluctuations have been tested in p-Pb and PYTHIA MC simulations. Also, different unfolding settings have been evaluated.

Charged Kaon Reconstruction in Au+Au-Collisions at 1.23 AGeV with HADES2h

In the energy regime of 1-2 AGeV, strangeness is produced below its nucleon-nucleon production threshold, this results in a steep excitation function. Due to their quark content, positive and negative kaons have different nucleon-nucleon production thresholds. Furthermore K$^{+}$ are supposed to feel a repulsive kaon nucleon potential, while K$^-$ can be resonantly absorbed by nucleons.
HADES, installed at GSI Helmholtzzentrum fuer Schwerionenforschung in Darmstadt, Germany, provides excellent capability to measure rare kaon signals. In April and May 2012, 7.3 billion Au(1.23 GeV per nucleon)+Au collisions have been recorded by HADES. In this contribution preliminary particle spectra of charged kaons will be presented. The results will be discussed with respect to the production mechanism.

In light of the recently realized possibility of hydrodynamic flow in small systems, we will study the charged particle pseudorapidity distribution as a function of collision centrality in the transition region between very peripheral and semi-central collisions, which still has not been carefully mapped out. Pseudorapidity distributions of charged particle production are important when characterizing the collision dynamics of relativistic heavy ions. We will compare systems with different collision geometry including Cu+Au, Au+Au, and U+U at top RHIC energy. The PHENIX silicon vertex detector will be used to make these measurements in the pseudorapidity interval of |$\eta$| < 2.

Quenching of high transverse momentum ($p_{\mathrm{T}}$) charged hadrons can be measured by the nuclear modification factor, which compares binary collision-scaled $p_{\mathrm{T}}$ spectra from central heavy-ion collisions to a reference spectrum, either proton-proton ($R_{\mathrm{AA}}$) or peripheral heavy-ion collisions ($R_{\mathrm{CP}}$), by taking their ratio. At $\sqrt{s_{\mathrm{NN}}}\ge$ 62.4 GeV the nuclear modification factor at high $p_{\mathrm{T}}$ is observed to be suppressed, i.e. less than unity, which is consistent with quenching. Measurements by STAR of charged hadron $R_{\mathrm{CP}}$($\sqrt{s_{ \mathrm{NN}}}$, $p_{\mathrm{T}}$) for $\sqrt{s_{ \mathrm{NN}}}$ = 7.7 - 200GeV show a smooth transition from strong enhancement of high $p_{\mathrm{T}}$ charged hadrons at $\sqrt{s_{ \mathrm{NN}}}$ = 7.7 GeV to strong suppression at $\sqrt{s_{ \mathrm{NN}}}$ = 200 GeV. These data will be compared with the event generators UrQMD, HIJING and AMPT. RHIC's broad range of collision systems and energies allow us to test the assumptions of the event generators; facilitating the investigation of the relative contributions from processes that lead to suppression and enhancement in heavy-ion collisions as a function of $\sqrt{s_{ \mathrm{NN}}}$.

Speaker:
Stephen Horvat
(STAR)

Slides

16:30

Charm quark dynamics in the QGP2h

We study the in- and out-off equilibrium dynamics of heavy quarks in the strongly interacting partonic and hadronic medium within the Parton-Hadron-String Dynamics (PHSD) transport approach [1] which incorporates explicit partonic degrees-of-freedom in terms of strongly interacting quasi-particles (quarks and gluons) in line with an equation of state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. The off-shell properties of quasi-particles- masses and widths - are described within the Dynamical Quasi-Particle Model (DQPM) and strongly depend on the temperature.
We calculate the different cross sections for perturbative partons (massless on-shell particles in the vacuum) and for dynamical quasi-particles (off-shell particles in the QGP medium as described by the DQPM) using the leading order Born diagrams [2]. We find that the finite width of the quasi-particles in the DQPM-which encodes the multiple partonic scattering - has little influence on the cross section for qQ ->qQ as well as gQ ->gQ scattering except close to thresholds. Thus when studying the dynamics of energetic heavy quarks in a QGP medium the spectral width of the charm quarks may be discarded.
Using the obtained on- and off-shell cross sections we have calculated the transport properties of the charm quarks in an equilibrated QGP such as the relaxation time [3], dynamical collisional energy loss, drag and diffusion coefficients, longitudinal and transverse momentum fluctuations, etc.
Finally we incorporate the charm scattering processes in the PHSD transport approach and study the dynamics of heavy quarks in realistic heavy-ion collisions addressing observables such as the elliptic flow v_2 and R_AA.
[1] W. Cassing, and E. L. Bratkovskaya, Nucl.Phys. A831 (2009) 215-242.
[2] H. Berrehrah, E. Bratkovskaya, W. Cassing, P.B. Gossiaux, J. Aichelin, and M. Bleicher, arXiv:1308.5148.
[3] H. Berrehrah, E. Bratkovskaya, W. Cassing, P.B. Gossiaux and J. Aichelin, arXiv:1311.0736.

Heavy-flavour probes of the quark-gluon plasma (QGP) have yielded a number of surprising results. Due to their large mass and the temperature scale of the collision,
it was anticipated that the charm and bottom quarks would interact weakly with the produced medium. It therefore came as a surprise when experimental results for D mesons indicated
charm quarks with small $R_{AA}$ and large elliptic flow $v_n$. This suggests that heavy-flavour probes are sensitive to the collective dynamics of the QGP medium which are now
well described by viscous hydrodynamics.
What is, however, not so well understood is the value of the coupling of the heavy quarks to the QGP medium. In this study, we couple the evolution of open charm quarks to
viscous hydrodynamics using a linearized Boltzmann equation [1] with pQCD based matrix elements for the heavy-quarks interacting with the QGP medium.
We compare the elastic energy loss transport coefficients $\hat{e}$ and $\hat{q}$ in this scheme for an infinite medium at finite temperature against those extracted using a Langevin equation
which describes the kinematics of the Boltzmann equation in the limit of small momentum transfer. We also examine the charm response to a thermal medium with fixed velocity profile, and present
first results for charm elastic energy loss in a realistic medium described by viscous hydrodynamics coupled to a hadronic afterburner [2].
[1] J. Auvinen, K. J. Eskola and T. Renk, Phys. Rev. C **82**, 024906 (2010).
[2] H. Song, S. A. Bass and U. Heinz, Phys. Rev. C **83**, 024912 (2011).

Speaker:
J. Scott Moreland
(Duke University)

Poster

16:30

Charmonia formation in quark-gluon plasma2h

Using the color evaporation model, the cross section for charmonium production in p+p collision is calculated in quark-gluon plasma.
The threshold energy for open charms is given by the free energy potential from lattice calculations, the initial charm quark pairs by the Pythia simulations, and their time evolution by solving the Langevin equation.
It is found that the threshold energy which decreases with temperature reduces the cross section while the invariant mass of charm pair which decreases by collisions enhances it.
As a result, charmonia production is suppressed by 30$\sim$50 % while $J/\psi$ production is similar or enhanced compared to in vacuum.

Speaker:
DrTaesoo Song
(Frankfurt Institute for Advanced Studies)

Slides

16:30

Chemical and Thermal analysis of LHC data within a blast-wave model with two freeze-outs2h

Within a blast-wave model which assumes two different freeze-outs, i.e. the chemical and thermal ones, both the hadron multiplicities and the transverse momentum spectra of various hadrons are analyzed in one model. In this calculation multiplicities of both the thermal hadrons and those decayed from resonances in a certain rapidity interval are calculated separately and the sum is fitted to the data. Usually the measured number of hadrons within a certain rapidity interval is converted into a number of hadrons in the whole rapidity region and the number in the whole rapidity region is regarded as a sum of the thermal ones and those decayed from resonances and fitted. This procedure is correct only when the rapidity distributions of both the thermal hadrons and the decayed ones are same.
Once the chemical analysis is done, by fixing the number of thermal hadrons of a certain species as the one at the chemical freeze-out, the transverse momentum spectra of various hadrons are fitted. Hence the adjustment of magnitudes of the pT spectra of various hadrons is not necessary.

Speaker:
Prof.Kang Seog Lee
(Chonnam National University)

Slides

16:30

Chemical Freeze-out Irregularities and Quark Gluon Bags Formation2h

We made a thorough analysis of the hadron resonance gas model
for the Breit-Wigner and for the Gauss resonance width parameterizations [1].
The latter model allows us to treat the usual hadrons and the quark gluon bags on the same footing and to study the stability of the results obtained within different formulations of the hadron resonance gas model.
Three versions of this model are fitted to reproduce 111 independent hadronic multiplicity ratios measured
for 14 values of the center of mass collision energies in the interval $\sqrt{s_{NN}} =$ 2.7--200 GeV. We found
that in a narrow range of collision energy $\sqrt{s_{NN}} =$ 4.3--4.9 GeV there exist the peculiar irregularities in various thermodynamic quantities calculated at chemical freeze-out. The most remarkable irregularity is an unprecedented jump of the number of effective degrees of freedom observed in this narrow energy range which is seen in all realistic versions of the hadron resonance gas model.
Thus, the ratio of the freeze-out entropy density to the cube of its temperature and
the ratio of the freeze-out pressure to its temperature to the fourth are, respectively, increased in 1.67 and 1.5 times, while the center of mass collision energy changes on about 14 \% (see figure below).
We are arguing that these irregularities evidence for the formation
of quark gluon bags. To understand such irregularities we study
the apparent width of wide hadronic resonances and quark gluon bags in a thermal medium.
We discuss
two new effects generated for the
wide resonances and quark gluon bags by a thermal medium near the threshold of decay:
their thermal enhancement and
their thermal sharpening.
We argue that the most optimistic chance to experimentally find the quark gluon bags may be related to their sharpening and enhancement in a thermal medium. In this case the wide quark gluon bags may appear directly or in decays as narrow resonances which are absent in the tables of elementary particles and which have the width of about 50-150 MeV and the mass of about or above 2.5 GeV.
1. K. A. Bugaev, A.I. Ivanytskyi, D. R. Oliinychenko, E. G. Nikonov, V. V. Sagun and G. M. Zinovjev,
arXiv:1312.4367 [hep-ph].

Chiral restoration and deconfinement in two-color QCD with two flavors of staggered quarks2h

In preparation of lattice studies of the two-color QCD phase diagram we study chiral restoration and deconfinement at finite temperature with two flavors of staggered quarks using an RHMC algorithm on GPUs [1]. We measure the chiral condensate and the corresponding chiral susceptibility as a function of the lattice coupling across the chiral transition. Using Ferrenberg-Swendsen reweighting we extract the maxima of the chiral susceptibility in order to determine pseudo-critical couplings on various lattices suitable for chiral extrapolations. These are then used to determine the relation between coupling and temperature.
[1] Scheffler, Schmidt, Smith, von Smekal, arXiv:1311.4324

Speaker:
MrDavid Scheffler
(TU Darmstadt)

Poster

16:30

Chiral superfluidity in QCD2h

In this talk I will discuss new effects due to the appearance of the chiral superfluidity in two regimes of QCD. First, at low temperatures and finite density, where the cold pion condensate under rotation and in electromagnetic fields develops string-like defects with anomalous currents flowing along them. Second, at low density and high temperatures, slightly above the deconfinement transition, where the quark-gluon plasma (QGP) can be described as a two-component fluid with the fermionic zero-modes forming the "superfluid" component carrying all the chiral properties of the QGP. The anomalous phenomena under consideration include the chiral magnetic, chiral vortical, axial vortical, chiral electric, chiral separation and other effects. I will also comment on the nature of their temperature dependence in both regimes.

Speaker:
Tigran Kalaydzhyan
(Stony Brook University)

16:30

CMS Jet reconstruction2h

We present the latest development of a particle-flow-based jet reconstruction and underlying event subtraction algorithm in heavy ion collisions with CMS. This new algorithm uses a data-driven method to estimate the underlying event level from the forward calorimeter energy distribution, taking into account possible flow modulation. Unlike jet-level subtraction methods, this approach produces a fully subtracted "hard event" as input to algorithms such as anti-kT, that automatically clusters to the hard jets. We show its improved performance to the CMS iterative pile-up subtraction, and also compare to other jet reconstruction strategies currently used in heavy ion collisions.

Speaker:
Yue Shi Lai
(Massachusetts Inst. of Technology (US))

Poster

16:30

Coalescence production of J/Psi in heavy ion collisions2h

It has been found that the nuclear modification factor of a J/Psi meson shows no significant dependence on centrality when going from Relativistic Heavy Ion Collider (RHIC) energy to Large Hadron Collider (LHC) energy, and it is believed that the regeneration of the J/Psi meson plays an important role in the production of J/Psi mesons. In this work we investigate the effects of the J/Psi meson production by charm quark coalescence on the nuclear modification factor in heavy ion collisions. We find that the charm quark coalescence of J/Psi meson is mainly responsible for the J/psi production in low transverse momentum region.

Speaker:
Sungtae Cho

16:30

Coherent $\psi$(2S) photo-production in ultra-peripheral Pb-Pb collisions at the LHC2h

Vector mesons are copiously produced in ultra-peripheral nucleus-nucleus collisions
In these collisions, the nuclei are separated by an impact parameter
larger than the sum of the nuclear radii.
The interaction proceeds through the emission of a photon, generated by the electromagnetic field of one of the two nuclei, fluctuating into a quark-antiquark pair,that interacts with the target nucleus.
The cross section for this process is sensitive to the gluon
distribution in the nucleus and can therefore probe the nuclear gluon shadowing.
The ALICE Collaboration has performed the first measurement of the
coherent $\psi$(2S) photoproduction cross section in Pb-Pb collisions at the LHC.
This charmonium excited state is tagged via the $\psi(2S) \rightarrow
l^{+} l^{-}$ and $\psi(2S) \rightarrow J/\psi\pi^{+}\pi^{-}$ decays,
where the $J/\psi$ decays into two leptons.
The measured cross section and its ratio to the $J/\psi$ cross
section are compared to predictions from theoretical models.

Speaker:
Michal Broz
(Czech Technical University (CZ))

Poster

16:30

Color Glass Condensate in Schwinger Keldysh QCD2h

Within the Schwinger-Keldysh representation of many-body QCD, it is shown that the leading quantum corrections to the strong classical color field is “classical” in the sense that the fluctuation field still obeys the classical Jacobi-field equation, while the quantum effects solely resides in the fluctuations of the initial field configurations. Within this context, a systematic derivation of the JIMWLK renormalization group equation is presented. A clear identification of the correct form of gauge transformation rules and the correct form of the matter-field Lagrangian in the Schwinger-Keldysh QCD is also presented.

Based on the quasiparticle model of the quark-gluon plasma (QGP), a color quantum path-integral Monte-Carlo (PIMC) method for calculation of thermodynamic properties and -- closely related to the latter -- a Wigner dynamics method for calculation of transport properties of the QGP are formulated. The QGP partition function is presented in the form of a color path integral with a new relativistic measure instead of the Gaussian one traditionally used in the Feynman-Wiener path integrals. A procedure of sampling color variables according to the SU(3) group Haar measure is developed for integration over the color variable. It is shown that the PIMC method is able to reproduce the lattice QCD equation of state at zero baryon chemical potential at realistic model parameters (i.e. quasiparticle masses and coupling constant) and also yields valuable insight into the internal structure of the QGP. Our results indicate that the QGP reveals quantum liquid-like rather than gas-like properties up to the highest considered temperature of 525 MeV. The pair distribution functions clearly reflect the existence of gluon-gluon bound states, i.e. glueballs, at temperatures just above the phase transition, while meson-like bound states are not found. The calculated self-diffusion coefficient agrees well with some estimates of the heavy-quark diffusion constant available from recent lattice data and also with an analysis of heavy-quark quenching in experiments on ultrarelativistic heavy ion collisions, however, appreciably exceeds other estimates. The lattice and heavy-quark-quenching results on the heavy-quark diffusion are still rather diverse. The obtained results for the shear viscosity are in the range of those deduced from an analysis of the experimental elliptic flow in ultrarelativistic heavy ions collisions, i.e. in terms the viscosity-to-entropy ratio.

A precise definition of the $Q\bar Q$ potential at high temperature
was obtained in the framework of effective field theories.
The potential was calculated in hard thermal loop resummed perturbation theory and happens to be complex [1].
In ref. [2] the definition was adapted to Euclidean lattice simulations but difficulties were encountered with the infinite real time limit required to extract the potential.
I will discuss how to disentangle precisely the short and long time physics from which the potential is defined [3]
and present a new method to perform the analytic continuation from Euclidean to real time [4].
After these improvements, the procedure to extract the potential produces precise results [5] and its application to quenched lattice QCD data [4, 6] gives us an estimate of both the real and imaginary part of the nonperturbative complex $Q\bar{Q}$ potential across the phase transition. The final results are very encouraging since the precision obtained for the real part of the potential is below the percent level. Even if only a rough estimate of the imaginary part is obtained in ref [4], we show that it could also be settled by more precise Euclidean data.
[1] M. Laine, O. Philipsen, P. Romatschke and M. Tassler, JHEP 0703 (2007) 054
[2] A. Rothkopf, T. Hatsuda and S.Sasaki, Phys. Rev. Lett. 108 (2012) 162001
[3] Y. Burnier and A. Rothkopf, Phys. Rev. D 86 (2012) 051503
[4] Y. Burnier and A. Rothkopf, Phys. Rev. Lett. 111 (2013) 182003
[5] Y. Burnier and A. Rothkopf, Phys. Rev. D 87 (2013) 114019
[6] Y. Burnier and A. Rothkopf, In preparation

Speaker:
DrYannis Burnier
(EPFL)

Poster

16:30

Concept and performance of the Silicon Tracking System for the CBM experiment at FAIR2h

The Silicon Tracking System (STS) is the central detector system of the CBM experiment. Its task is to perform track reconstruction and momentum determination for all charged particles created in beam-target collisions at SIS 100 and SIS 300 beam energies. The technical challenges to meet are a high granularity matching the high track densities, a fast self-triggering read-out coping interaction rates up to 10 MHz, and a low mass to yield high momentum resolution.
We introduce the concept of the STS, being comprised of eight tracking stations employing double-sided silicon microstrip sensors on modular structures that keep the read-out electronics outside the physics aperture. The detector system acceptance covers polar angles between 2.5 and 25 degrees and will be operated in the 1 T field of a super conducting dipole magnet. The performance of the STS with respect to hit finding, track reconstruction and momentum resolution are shown based on simulation studies using a realistic geometry and detector response based on the evolving engineering and prototyping effort.

The recent LHC and Tevatron data for inclusive high-$p_T$ charged hadron production in p+p(${\rm \bar{p}}$) collisions show a discrepancy in comparison to the NLO perturbative QCD predictions with modern fragmentation functions (FFs). We have quantified this observation by a systematic comparison between the calculations with different FF sets and data for several collision energies [1]. We show that especially the predictions with the most recent FFs clearly overshoot the high-$p_T$, high-$\sqrt{s}$ data even when the scale variations, and uncertainties in the PDFs and FFs are accounted for. We conclude that this behavior is due to the too hard gluon-to-hadron FFs, which calls for a complete re-analysis of the FFs using the high-$\sqrt{s}$ data at $p_T > 10\,\rm{GeV}$ where the theoretical uncertainties are only modest. We discuss also to what extent these discrepancies affect the interpretation of the LHC p+Pb collision data.
[1] D. d'Enterria, K.J. Eskola, I. Helenius and H. Paukkunen, *Confronting current NLO parton fragmentation functions with inclusive charged-particle spectra at hadron colliders*, arXiv:1311.1415 [hep-ph], submitted to Nucl. Phys. B.

The conserved charge fluctuations, as quantified by the corresponding susceptibilities, provide important information about the charge-carriers and their dynamical correlations in strongly interacting matter such as the quark-gluon plasma. Using the gauge-gravity correspondence approach, we study the patterns of conserved charge fluctuations in two types of holographic models for QCD, the D4/D8 and the D3/D7 models. We compute and compare the quark number susceptibilities in both models and find an interesting common feature of the two: at very strong coupling higher order susceptibilities are suppressed and the conserved charge fluctuations become purely Gaussian. In light of the state-of-the-art lattice QCD results we also discuss what we can learn from these susceptibilities about the underlying degrees of freedom in the $1\sim 2 T_c$ quark-gluon plasma and examine the viability of different ideas such as holography, quasi-particles, as well as bound states. From analysis of second order cross-flavor susceptibilities we conclude that the bound states exist and are important in the $1\sim 2 T_c$ region. Based on that we have further constructed model with predictions for several ratios of fourth-order susceptibilities that are in good agreement with lattice QCD results.
Reference: Shuzhe Shi and Jinfeng Liao, JHEP06(2013)104[arXiv:1304.7752].

Speaker:
Shuzhe SHI
(Tsinghua University)

Poster

16:30

Constraining dissipative corrections to particle distributions at freeze out from anisotropic flow2h

A decoupling dissipative fluid emits particles differently from an ideal one. The modification can be estimated with the help of a saddle-point calculation, which amounts to the limit of a low freeze-out temperature. Computing the anisotropic flow coefficients, we show that relations between different harmonics valid in the ideal case for particles with a higher velocity than the fluid no longer hold. This may be exploited to actually constrain the functional shape of the dissipative corrections, and thereby the transport coefficients of the fluid at freeze out.

Speaker:
Nicolas Borghini
(University of Bielefeld)

Poster

16:30

Constraining global initial geometry with directed flow2h

Hydrodynamic simulations together with models for the fluctuating initial
conditions lead to a good description of experimental data on all flow
harmonics. To complement these analyses which allow to constrain initial
fluctuations, one can use rapidity-odd directed flow to unravel the global initial geometry.
We discuss what properties of the tilt of the initial state is necessary to
reproduce data on v1(y) and v1(b). We argue that skewness
(asymmetry in the transverse overlap region) of the initial state is needed to reproduce data on v1(pt). We conclude by computing tilt and skewness of various initial conditions and showing which are consistent with data on rapidity-odd directed flow.

We propose a systematic approach for constraining models of initial conditions using a combined analysis of elliptic $v_2$ and triangular $v_3$ flow data with viscous hydrodynamic calculations. For $v_2$ and $v_3$ harmonics the hydrodynamic response to the initial state is dominated by linear response, which means $v_2$ is proportional to the ellipticity $\varepsilon_2$ and $v_3$ is proportional to the triangularity $\varepsilon_3$, i.e. $v_n = C_n\varepsilon_n$, where $C_n$ is the linear response coefficient. Experimental data on elliptic and triangular flow, combined with the calculation of $C_n$ in relativistic hydrodynamics, provide us with rms values of initial anisotropies $\varepsilon_2$ and $\varepsilon_3$. By varying free parameters in hydrodynamic calculations, we get an allowed region in the (rms $\varepsilon_2$, rms $\varepsilon_3$) plane. Thus we are able to compare Monte Carlo models of the initial state with the allowed region and exclude several of these models. We provide a simple test that can be performed on any candidate model to determine its compatibility with data. We also illustrate that the effect of changing the granularity of the initial state is similar to changing the medium properties, making these effects difficult to disentangle using only these data.
[Reference: E. Retinskaya, M. Luzum and J. -Y. Ollitrault, Phys. Rev. C 89, 014902 (2014)]

Speaker:
Ekaterina Retinskaya
(CEA)

Poster

16:30

Constraining the vector interaction strength of QCD2h

We show how repulsive interactions of deconfined quarks as well as confined hadrons can be constrained in a straight forward way by model comparisons of baryon number susceptibilities with lattice QCD results . We also discuss implications for earlier constraints, extracted from the curvature of the transition line of QCD and compact star observables. Our results clearly point to a strong vector repulsion in the hadronic phase and near-zero repulsion in the deconfined phase.

Two-particle correlations have been widely used as a tool to explore particle production mechanisms in heavy ion collisions. The mixed-event method is generally considered as a standard method to correct correlation functions for effects of finite acceptance. We demonstrate that additive correlated signals, such as jets, are distorted by the mixed-event method and propose new methods for more accurate finite-acceptance corrections and background-rejection effects. Correlation functions from the mixed-event method and the proposed new methods are compared through particle-level PYTHIA simulations containing well-defined correlation signals. Significant differences are observed at large $\Delta\eta$ in general and especially in the case of an asymmetric particle distribution like that observed in proton-lead collisions. The applicability and validity of the new methods are discussed in detail.

Speaker:
Saehanseul Oh
(Yale University (US))

Poster

16:30

Cross section fluctuations in hadronic nad nuclear collisions2h

The nucleon-nucleon collision profile, being the basic entity
of the wounded nucleon model, is usually adopted in the form
of hard sphere or the Gaussian shape.
It has been noticed recently [1] that the cross section fluctuations,
given by the gamma distribution, lead to the profile function
which smoothly ranges between the both, above mentioned, limiting forms.
Nucleon-nucleon cross section fluctuations have been evaluated from
the elastic differential cross section, multiplicity fluctuations and
attenuation of cosmic rays. Energy dependence of cross section
fluctuations has been compared with model predictions and other existing
estimates.
Examples of some initial state characteristics (fluctuations
of target participants, cross sections dependence of mass number
and energy, among others) of proton-nucleus and nucleus-nucleus
collisions at wide range of center of mass energies demonstrating
sensitivity on cross section fluctuations will be discussed.
[1] M. Rybczynski and Z. Wlodarczyk, J. Phys. G41 (2014) 015106.

Speaker:
Maciej Rybczynski
(Jan Kochanowski University (PL))

Slides

16:30

Cumulative Particle Production in p+A Collisions and z-Scaling2h

Experimental data on inclusive charged particle spectra in p+A collisions are analyzed in the framework of z-scaling. The data on cross sections were taken by groups of G.Leksin at FNAL (Batavia), L.Zolin and V.Gapienko at IHEP (Protvino) with nuclear targets from beryllium up to tungsten. Spectra cover a special kinematics known as a cumulative region. Cumulative particles can be only produced in nuclear collisions. Their production is assumed to be sensitive to the state of the nuclear matter formed at the extreme conditions. Theory of z-scaling is developed for analysis of the cumulative processes and search for phase transition effects. The concept of z-scaling is based on principles of self-similarity, locality and fractality of constituent interactions at small scales. The momentum spectrum of the inclusive particle is recalculated to scaling function Ψ(z) which depends on self-similarly parameter z. A microscopic scenario of pA interactions in terms of momentum fractions x1, x2 is discussed. Results of the analysis are compared with the noncumulative data on high-pT hadron production in pA collisions obtained by J.Cronin, R.Sulyaev and D.Jaffe groups. Universality of the shape of function Ψ(z) is used to predict inclusive cross sections of particles produced in the deep-cumulative region.

Models for the heavy flavor production in ultrarelativistic heavy ion
collisions suffer from a lack of elliptical flow as compared to the experimental data if they reproduce $R_{\rm AA}$, often referred to by experimentalists as a "tension between $R_{\rm AA}$ and $v_2$". One possible reason for this discrepancy may be the disregard of D-meson rescattering in hadronic matter in the latest stage of the evolution. To study this is the core of our contribution.
The drag and diffusion coefficients of D-mesons propagating in a hot and dense hadronic matter are calculated. The hadronic medium consists of pions, kaons, etas, rho-mesons and nucleons. We find that the transport coefficients increase with the temperature of the medium. The dominant contributions to the drag and diffusion coefficients come from pions, but at higher temperatures the contributions from other (heavier) hadrons become important as well. In addition, we evaluate the thermal relaxation rate of D-mesons, which is in agreement with the model estimate of He, Fries and Rapp. The relaxation rate reaches approx. 0.1/fm in the vicinity of the critical temperature; this is comparable to non-perturbative T-matrix calculations of charm-quark relaxation in QGP. The size of the transport coefficients in hadronic matter shows that the hadronic contributions should be included when evaluating the nuclear suppression factor and the elliptic flow for single leptons originating from the decays of D-mesons or for D-mesons during the expansion of the matter created in heavy ion reactions at mid-rapidity.
Finally, we study the consequence for the $R_{\rm AA}$ and $v_2$ of heavy mesons by using a hydrodynamical model for the expansion of QGP and the hadron gas in which the chemical freeze-out is modelled by the effective chemical potential. We present the modification of the $R_{\rm AA}$ and $v_2$ of D-mesons due to the hadronic rescattering, for both, RHIC and LHC energies.

Speaker:
DrVitalii OZVENCHUK
(subatech)

16:30

DCA and secondary vertex measurement of electron pairs using PHENIX-VTX2h

The bottom quark is a powerful probe to study the characteristics of
QGP created in the high energy heavy ion collisions.
The bottom production can be measured using the non-prompt $J/\psi$ from B
decays (B -> $J/\psi$ + X).
It is possible to identify the $J/\psi$ through electron pairs measuring
a displaced vertex position using the silicon vertex detector (VTX).
In this poster, we will report the current status of the analysis measuring
the DCA and secondary vertex of electron pairs from non-prompt $J/\psi$
decays with PHENIX-VTX.

Speaker:
DrTakashi Hachiya
(RIKEN)

Poster

16:30

Deconfinement phase transition with heavy quarks2h

We explore the influence of heavy quarks on the deconfinement phase transition in an effective model for gluons interacting with dynamical quarks in color SU(3). With decreasing quark mass, the strength of the explicit breaking of the Z(3) symmetry grows and the first-order transition ends in a critical end point (CEP). The nature of the critical endpoint is examined by studying the longitudinal and transverse fluctuations of the Polyakov loop, quantified by the corresponding susceptibilities. The longitudinal susceptibility is enhanced in the critical region, while the transverse susceptibility shows a monotonic behavior across the transition point. We also investigate the dependence of the CEP on the number of quark flavors at zero and finite quark density. Finally we confront our model results with lattice calculations and present a formula linking the hopping parameter to the quark mass.

Speaker:
DrLo Pok Man
(GSI)

Poster

16:30

Description of ${\langle p_{\mathrm{T}}\rangle}$-${N_{\mathrm{ch}}}$ correlations in pp, pA and AA collisions in Monte Carlo model based on the interaction of color dipoles2h

The correlation between the mean transverse momentum and the multiplicity of charged particles,
recently measured by the ALICE experiment in
${{\mathrm {p\kern-0.05em p}}}$, ${{\mbox{p-Pb}}}$ and ${{\mbox{Pb-Pb}}}$ collisions
at LHC,
is studied in the framework of string-parton Monte-Carlo model, in which the elementary collisions are realized
by interactions of color dipoles.
It enables to describe pA and AA scattering without referring to the Glauber picture of independent nucleon
collisions and to include the account of string fusion as a source of collectivity effects.
The model reproduces multiplicity yields in wide energy range (from ISR to LHC)
as well as the centrality dependence of multiplicity in ${{\mbox{Pb-Pb}}}$ collisions.
The results obtained in the framework of the model
for ${\langle p_{\mathrm{T}}\rangle}$-${N_{\mathrm{ch}}}$ correlations
describe the main features of the experimental data.
The contribution of different mechanisms to ${\langle p_{\mathrm{T}}\rangle}$-${N_{\mathrm{ch}}}$
correlation is analyzed.

High $p_{T}$ hadrons as fragments of hard scattered patrons
are a powerful tool to probe the opacity of the system
produced in nucleus collisions, through the loss of their
momenta in the medium created. In the last decade, the
momentum loss was quantified in terms of suppression of
the yield at given $p_T$. We recently measured the
fractional momentum loss ($\delta p_{T}/p_{T}$, where
$p_T$ being original momentum of a hadron, and
$\delta p_T$ being the loss of its momentum in the medium)
of the hadrons statistically, and found that the partons
lose 1.5 times larger $\delta p_{T}/p_{T}$ in central
2.76TeV Pb+Pb collisions at the LHC than that in 200GeV Au+Au
collisions at RHIC. We are extending the $\delta p_{T}/p_{T}$
measurement over different collisions species and cms energies
to study a systematic trend.
It is also interesting to see how the trend connects to the
smaller systems like $d(p)$+A collisions which recently have
revealed their possible collective nature. The measurement of
emission angle dependent momentum loss of hadrons would also be
interesting in the systems.
We will report a detail investigation of parton energy loss in
$d(p)$+A and A+A systems using high $p_T$ hadrons.

We study the transport property of charm quarks at finite temperature in
quenched lattice QCD with improved maximum entropy method (MEM).
We extend the MEM analysis to the product space of spectral functions at more
than two different momenta to take advantage of more data and the strong
correlation among Euclidean correlators with different momenta.
We find that this method drastically reduces the error of the reconstructed
images, in particular, at small energy.
We apply this method to extract the diffusion coefficient of charm quarks.
We also perform an error estimate of the result, which has not been carried
out correctly in previous analyses.
Our analysis gives finite diffusion coefficients with statistical
significance and small errors.
Our method and result on the basis of first principle calculations will shed
light on understanding on the dynamics of heavy quarks in QGP.

Speaker:
MrAtsuro Ikeda
(Osaka University)

Poster

16:30

Determination of tolerances of mirror displacement and radiator gas impurity for the CBM RICH detector2h

The Compressed Baryonic Matter (CBM) experiment will be a dedicated heavy-ion experiment at the future FAIR facility. In order to identify electrons, a RICH detector and several layers of TRDs will be employed. The RICH detector will be operated with CO2 as a radiator gas, a spherical glass mirror plane, and MAPMTs as photon detectors. The mirror system consists of about 70 square mirror tiles of an area of about 40x40 cm2 each. To verify the developed RICH concept a laterally scaled prototype has been constructed, in which all modules of the main components have approximately the same dimensions and properties as foreseen for the full detector. The mirror system of the prototype consists of four tiles, which enables studies of mirror-boarder effects on Cherenkov rings and their reconstruction and fit quality. The prototype has been implemented in the CBM software framework with realistic properties of the detector components. Its performance has been simulated and measured during beam times at the CERN-PS facility with electron-pion beams of momenta between 2 and 10 GeV/c.
Besides many important aspects that guaranty successful operation of the detector, the determination of upper limits of gas impurity and mirror displacements have systematically been simulated and measured. The results will be presented in this contribution.

Using next-to-leading order perturbative QCD and a conjecture of saturation to suppress the production of low energy quanta, we calculate the initial energy densities and formation times for the dissipative fluid dynamical evolution of the quark-gluon plasma produced in ultrarelativistic heavy ion collisions [1,2].
We identify the uncertainties of the model and demonstrate the predictive power of the approach by obtaining a good global agreement with the measured centrality dependence of the charged particle multiplicities, transverse
momentum spectra and elliptic flow simultaneously for the Pb+Pb collisions at the LHC and Au+Au at RHIC. In particular, the shear viscosity-to-entropy ratio in the different phases of QCD matter is simultaneously constrained by all these data. In order to study higher cumulants $v_n$ and their event-by-event (EbyE) distributions, we are currently engaged in modeling the EbyE fluctuations of saturated minijet production in this framework [3]. Also these results will be reported.
[1] R. Paatelainen, K. J. Eskola, H. Holopainen and K. Tuominen, **Phys. Rev. C87** (2012) 044904
[2] R. Paatelainen, K. J. Eskola, H. Niemi and K. Tuominen, **arXiv:1310.3105** [hep-ph], to appear in **Phys. Lett. B**
[3] H. Niemi, K. J. Eskola, R. Paatelainen and K. Tuominen, work in progress

Speaker:
Risto Paatelainen
(University of Jyväskylä)

Poster

16:30

Development of fast ramped superconducting magnets for SIS3002h

SIS300 is the second of the two planned new synchrotrons at FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. The high field values of up to 4.5 T for the dipoles require a so called $\cos{(\Theta)}$ design. The ramp rate of these magnets is 1 T/s, therefore special attention has been taken on the reduction of AC losses and the mechanical integrity of the magnets. For this, for example, new superconducting wires with small filament sizes of about 3 µm and a resistive CuMn matrix between the filaments has been developed. A full size model of a short curved dipole (4.5 m long) was designed, built and tested in a collaboration of GSI with groups of INFN in Genova, Milano and Salerno. Also two quadruple magnets and a steering dipole have been produced and successfully tested at IHEP, Protvino. The magnet design activities over the past years as well as an outlook into the future will be summarized.

Development of prototype components for the Silicon Tracking System of the CBM experiment at FAIR2h

The building block of the CBM Silicon Tracking System is a detector module comprising double-sided silicon microstrip sensors, ultra-thin read-out cables, and novel front-end electronics. Various types of modules will be employed in the detector system, differing in sensor size and cable length.
We report on the development of the module components. The silicon sensors have a CBM specific layout. The performance of recent full-size prototypes will be presented. The cables are stacks of two low-mass signal layers, based on fine-pitch aluminum lines, and spacers. They bridge the distance between the sensors and the read-out electronics. The electronics comprises self-triggering ASICs. The integration of sensors, read-out cables and electronics into detector modules has been realized. We summarize the construction and performance of recent prototypes.

Speaker:
Pradeep Ghosh
(GSI)

Poster

16:30

Development of the photon detection system for the CBM RICH2h

The CBM-RICH detector is an essential component of the
CBM experiment which will be build at the Facility for Antiproton
and Ion Research, FAIR, in Darmstadt.
It will serve for electron identification and pion suppression
for particle momenta up to ~8 GeV/c.
Pion suppression by up to 4 orders of magnitude is necessary in
order to get access to rare di-electron decays of light vector mesons,
such as the rho meson, one of the key observables to study the
highly compressed matter produced in the heavy ion collision process.
The CBM-RICH detector will use CO2 gas as radiator medium. Spatially resolved
detection of Cherenkov photons will be achieved using Multianode
Photomultipliers (MAPMT) or Microchannel plate detectors (MCP).
Only these devices can provide sufficient detection efficiency,
time resolution and rate capability necessary to operate the CBM
experiment at Au-Au interaction rates up to 10 MHz.
We have studied and compared in detail different sensor options,
such as the 2x2 inch Hamamatsu H8500, the new H12700, the 1x1 inch
R11265, or the XP85012 MCP from Photonis.
Single photon XY scans combined with a self triggered readout
system allow to achieve many different performance
parameters, such as efficiency, cross talk, and dark noise in a single
lab measurement.
During two test beam campaigns with a CBM-RICH prototype detector
at CERN-PS we could compare the different sensor options in beam.
In this poster, we present our studies with respect to the photon
detection system for the CBM-RICH detector.

Speaker:
Christian Pauly
(Bergische Universitaet Wuppertal (DE))

Poster

16:30

Di-electron reconstruction in Au+Au@1.23 GeV/u2h

Systematic studies of di-electron and strangeness production in the few GeV per nucleon energy regime have been performed in the past years with the High Acceptance Di-Electron Spectrometer, installed at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.
In the most recent measurement, di-electron production for the heaviest collision system, Au+Au at the top SIS18 beam kinetic energy of 1.23 GeV/u have been investigated. For the first time in such a collision, where long lifetimes of the fireball are expected, the di-lepton signal has been obtained.
Pure electron identification has been achieved by exploring information from the Ring Imaging Cherenkov detector together with a time-of-flight measurement and with an electromagnetic cascade signature in the Pre-Shower detector. Decision is taken upon the response of a neural network trained with high purity tracks. Topological cuts are used to suppress combinatorial background.
In this contribution we will present details of signal extraction and the investigations of its purity based on detailed Monte Carlo studies. Furthermore, in order to extract signal form non-trivial pairs a combinatorial background has to be suppressed.
The work is supported by VH-NG-823, BMBF (06FY9100I and 06FY7114), HIC for FAIR, EMMI, GSI, HGS-HIRe and H-QM.

Correlated unlike sign dielectrons provide important and relatively clean information to access the properties of the hot and dense matter, the Quark-Gluon Plasma (QGP), created in relativistic heavy-ion collisions. Once they are produced, they traverse the fireball without interacting strongly with the medium. The collective behaviour of the dielectrons with respect to a global event plane provides rich information of the initial stage of the expanding fireball where flow starts developing.
In the central barrel ($|\eta|<0.8$) of the ALICE experiment, electrons (and positrons) can be detected and identified by the Inner Tracking System, the Time Projection Chamber and the Time-Of-Flight. For the study of the dielectron elliptic flow at mid-rapidity, the VZERO scintillators at forward rapidity are used for event plane estimation to avoid auto-correlations.
In this poster, a first attempt to measure the elliptic flow of dielectrons in Pb--Pb collisions at $\sqrt{s_{\mathrm {NN}}} = 2.76$ TeV with the ALICE experiment is presented. An effort is put into removing the background $v_2$ from uncorrelated unlike sign dielectrons with the mixed-event approach. A comparison to the elliptic flow of identified particles measured in the same system, as well as measurements from experiments at RHIC will be discussed. This work is expected to be the first step towards the measurement of the elliptic flow of thermal photons radiated from the fireball, which is regarded as a unique probe to study the formation time of the QGP.

Speaker:
Hongyan Yang
(University of Utrecht (NL))

16:30

Dielectron production in Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200GeV at STAR2h

We report the STAR newest measurement of dielectron production in
Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200GeV. The data sets
used in the analysis include large samples collected in 2010 and 2011
for Au+Au and 2012 for p+p which both yield about a factor of 3 more
statistics compared to previously reported STAR results.
We present the centrality and $p_{T}$ dependence of dielectron production
from low-mass ($M_{ee}$<1.1 $GeV/c^{2}$)
and intermediate-mass (1.1<$M_{ee}$<3 $GeV/c^{2}$)
regions. The results were measured in the STAR acceptance at midrapidity
with full azimuth coverage. The measurements are compared with various
models to gain insight of underlying physics. Furthermore, we report
the preliminary results of dielectron azimuthal correlation in the
intermediate-mass region in Au+Au and p+p collisions at $\sqrt{s_{NN}}$
= 200GeV and compare the data with model calculations.

Deep inelastic scattering is a powerful tool to
study the structure of hadrons and test our understanding of the strong
interaction. The precise proton structure
function measurements done at HERA have been a crucial test for
the Color Glass Condensate effective field
theory description of the high energy hadronic interactions.
Ideally one would want to continue the analysis with nuclear targets where
gluon saturation effects are expected to be even stronger.
Because the role of the electron in DIS events is to only act as a source of virtual
photons, one can study the same physics in ultraperipheral (large impact
parameter) heavy ion collisions. In these events the dominant process is the
one where one nucleus acts as a photon source, and one is left with a
similar photon-nucleus scattering as in DIS.
Recently diffractive vector meson production in ultraperipheral collisions has
gained a lot of theoretical and experimental attention, because the cross section
is especially sensitive to the saturation effects and also probes the spatial
distribution of gluons. For example the ALICE collaboration has measured the
diffractive J/Psi cross sections in lead-lead collisions [1].
We calculate coherent and incoherent diffractive vector meson production from
the Color Glass Condensate framework and compare our results and predictions
with the ALICE data. We discuss the dependence on the vector meson properties and
the modelling uncertainties. We also present predictions for proton-nucleus
collisions. [2]
[1] ALICE collaboration, Phys. Lett. B718 (2013) 1273,
Eur.Phys.J. C73 (2013) 2617
[2] T. Lappi, H. Mäntysaari, Phys.Rev. C87 (2013) 032201,
Phys.Rev. C83 (2011) 065202

The hybrid model HYDJET++, including soft and hard physics, is employed for the analysis of azimuthal anisotropy harmonics and dihadron angular correlations measured in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The soft part of the model represents a thermal hadron production at the freeze-out hypersurface in accordance with hydrodynamical calculations. The possible triangular shape fluctuation of the initial overlap density of the colliding nuclei was implemented in HYDJET++ by the modulation of the final freeze-out hypersurface with the appropriate triangular coefficient, which results in triangular flow $v_3$. Along with elliptic flow $v_2$, it generates higher order flow coefficients, as well as a specific structure of dihadron angular correlations on relative azimuthal angle in a broad range of relative pseudoraidities ($\Delta\varphi \Delta\eta$). The comparison of model results with the LHC data on short- and long-range angular correlations is presented for different collisions centralities and transverse momenta intervals.

We extend to study the dilepton emission from heavy -ion collision of Quark-gluon Plasma incorporating the chemical potential and temperature dependent on quark mass. The dilepton emission rate is found to be enhanced in comparison to the earlier result of only temperature dependent value of quark mass and in comparison to other theoretical calculations. The study finds that the emission rate of dilepton through the chemical potential is increasing function depending on increasing value of chemical potential ranging
from $\mu = 100 -450~$ MeV. This indicates that the overall result of dilepton emission through both temperature and chemical potential will provide better information about the signature of forming Quark-Gluon Plasma with this quasi-model quark mass.
Keywords: Dilepton; Quark-Gluon Plasma

Speaker:
DrSomorendro Singh Shougaijam
(University of Delhi, Delhi)

16:30

Dimuon Production in Au+Au √sNN = 200 GeV Collisions at STAR2h

Dimuon production, which is sensitive to the early stage of heavy-ion collisions, provides a unique tool to study the Quark-Gluon Plasma.
At low invariant mass, the dimuon mass spectrum has the contributions from many mesons, such as $\eta$, $\omega$, $\eta\prime$. At the same time, the background from $\gamma$ conversion is largely suppressed compared to the background from dielectron measurement.
With the Time Projection Chamber and the Time of Flight detector together, the STAR experiment at RHIC has good muon identification at low momentum ($<$0.3 GeV/$c$) with full azimuthal coverage at mid-rapidity. We present the preliminary results of the low-mass dimuon ($<$0.65 GeV/$c^2$) distribution at mid-rapidity $|y|<1$ and compare to hadronic cocktails at Au$+$Au $\sqrt{s_{NN}} = $ 200 GeV.

Direct photons are emitted from various processes from all stages from the beginning to the end of the high energy heavy ion collisions.
Theoretical models tell that the angular emission patterns of the photons are different depending on their production mechanism.
Previous published PHENIX results indicate that the second order Fourier coefficient ($v_{2}$) is positive for $p_{T}$<4.0GeV/c, which is qualitatively explained by hydrodynamical model calculations, but not quantitatively.
The 3rd order Fourier coefficient ($v_{3}$) of photons has been proposed as a critical additional handle to understand photon emission.
Photons emitted under the presence of strong magnetic field created in the collision would have a significant influence on $v_{2}$ and very little on $v_{3}$.
In contrast, hydrodynamical models predict a sizable photon $v_{3}$.
We report the latest results on the direct photon $v_{2}$ and $v_{3}$ coefficients in Au+Au collisions at $\sqrt{s_{NN}}$=200GeV.

Disentangling the soft and hard components of the pp collisions using the spheri(o)city approach2h

The complexity of the proton-proton interactions requires many theoretical models to describe the different features of the data. Typically, they are incorporated in MC event generators and their parameters are tuned to describe the average behaviour of specific quantities. However, this approach does not allow to understand in detail the impact of the different components in the measurable observables. This task is particularly important to really understand the physics of the hadronic interactions which so far have been taken as the baseline to learn about the medium created in ultra-relativistic heavy ion collisions.
In this work a new method to extract meaningful information from the pp data is proposed, the aim is to use observables sensitive to e.g. partonic stages where collective effects are possible. The approach is based on the use of the event structure variables (sphericity and spherocity). This was developed in the framework of Pythia 8.180 since its pQCD content seems very well adapted for this goal. For minimum bias pp collisions at $\sqrt{s}=0.9$ and 7 TeV a discussion of the interconnection among event shapes, multi-parton interactions, abundances of final semi-hard quarks/gluons and color reconnection, is done. A study of the identified particle transverse momentum, $p_{\rm T}$, spectra and their ratios will be presented for isotropic (soft) and jetty-like (hard) events; and as a function of multiplicity. The results indicate that the baryon-to-meson ratio for soft events is larger than for the jetty-like ones, the latter case gives particle ratios compatible with NLO. The observations are explained in terms of the competition between gluons and quarks for the particle production at intermediate $p_{\rm T}$. The results are compared to LHC data and the similarities between the observed effects and those measured in pp and Pb-Pb collisions are discussed.

Speaker:
Antonio Ortiz Velasquez
(Universidad Nacional Autonoma (MX))

Slides

16:30

Domain growth and fluctuations during quenched transition to quark-gluon plasma2h

We model the initial confinement deconfinement transition in relativistic heavy-ion collisions as a rapid quench in view of expected rapid thermalization to a quark-gluon plasma state. The transition is studied using the Polyakov
loop model, with the initial field configuration (in the confining phase) covering a small neighborhood of the confining vacuum l= 0, as appropriate for
T < Tc. Quench is implemented by evolving this initial configuration
with the effective potential at a temperature T >Tc. We study the formation of Z(3) domain structure and its evolution during the transition as l rolls down in different directions from the top of the central hill in the effective
potential of l. When explicit Z(3) symmetry-breaking effects (arising from dynamical quark effects) are small, then we find well defined Z(3) domains, which coarsen in time. Remarkably, the magnitude plot of l shows
vacuum bubble like configurations arising during the quench. This first-order transition like behavior occurs even though there is no metastable vacuum separated by a barrier from the true vacuum for the parameter values used.
When the initial field configuration everywhere rolls down roughly along the same direction (as will happen with large explicit symmetry breaking) then we do not find such bubble like configurations. However, in this case
we find huge oscillations of l with large length scales. We show that such large oscillations can lead to large fluctuations in the evolution of flow anisotropies compared to the equilibrium transition case.

Speaker:
DrRanjita Mohapatra
(Physical Research Laboratory)

Poster

16:30

Dynamical simulation of a linear sigma model near the critical point2h

The intention of this study is the search for signatures of the chiral phase transition and the impact of non-equilibrium effects.
To investiage the impact of fluctuations, e.g. on the baryon density, near the chritical point or the chiral phase transition of QCD, we developed a 3+1D numerical, non-equilibrium simulation of an effective linear sigma model. Chiral fields are approximated as classical fields, quarks are described by quasi-particles via a Vlasov equation. For additional dynamics, kinetic quark-quark and chemical quark-sigma interactions have been implemented. The challenge is the consistent description of hard interactions between particles and classical fields. Therefore a new Monte-Carlo-Langevin-like formalism has been developed and is discussed.

Speaker:
Christian Wesp
(Goethe Universität Frankfurt)

Poster

16:30

Early thermal and chemical equilibration of quarks and gluons2h

Local equilibration of a QCD medium has been a long-standing issue in hadron physics since the discovery of a nearly-perfect fluid in heavy-ion collisions at RHIC and LHC. The pre-collision state is considered to be described as color glass condensate, which has a relatively large number of high-momentum gluons but almost no quarks. The success of hydrodynamic approaches, on the other hand, indicate that the medium should quickly turn into an equilibrated quark-gluon plasma in less than 1 fm/$c$.
Equilibration of a heavy-ion system requires (i) isotropization, (ii) thermalization and (iii) chemical equilibration of partons. In this work we focus on the latter two and aim to provide an efficient description for producing low-momentum quarks and gluons by modeling collinear parton splitting and recombination processes. Parton-medium interaction, which is required for creating off-shell partons, is embedded in the model by drag and diffusion effects in relativistic Fokker-Planck equation. We perform numerical simulation in a transverse direction for qualitative analyses to find that the gluon distribution approaches the thermal one in a very short time, and quark thermal/chemical equilibration is slower than the gluon thermalization though it is reasonably fast. The recombination is suggested to be essential in chemical equilibration as quark production from over-populated low-momentum gluons would be suppressed by Pauli exclusion principle. The results imply that the collinear processes play an important role in early thermal and chemical equilibration of the QCD matter produced in high-energy heavy-ion collisions.

Speaker:
DrAkihiko Monnai
(RIKEN BNL Research Center)

Poster

16:30

Effect of the equation of state on particle spectra, elliptic flow and HBT radii2h

We present results of a systematic study of the role of the equation of state in the hydrodynamic model. By using the same initial conditions and freeze-out scenario, the effects of different equations of state are compared by calculating their respective hydrodynamical evolution, particle spectra, elliptic flow and HBT radii. Three different types of equation of state are studied, each focusing on different features, such as nature of the phase transition, strangeness and baryon densities. Different equations of state imply different hydrodynamic responses, the impact thereof on final state anisotropies are investigated. The results of our calculations are compared to the data from RHIC at 130 GeV and 200 GeV. It is found that the three equations of state used in the calculations describe the data reasonably well; differences can be observed, but they are quite small. The insensitivity to the equation of state seems to weaken the need for a locally thermalized description of the system, at least for the observables analyzed in this work. A precise determination of transport coefficients by fitting collective flow parameters in the framework of hydrodynamics still requires caution.